There are many places you might expect to find an A-list star in Hollywood, but a scruffy dance studio at the wrong end of the Walk of Fame isn’t the first that springs to mind. The homeless and the addicted hustle the star-spotting tourists who wander wide-eyed into souvenir shops selling Michael Jackson memorabilia, utterly unaware that, two floors above them, his youngest sister is rehearsing the choreography for her new single, Make Me.

“I love the natural light,” says Janet Jackson, nodding towards the huge windows that look out onto the gritty streets below. She’s devoid of make-up and dressed in black tracksuit bottoms and a grey cashmere top, a low-key look that matches the location. There is no big entourage in tow, either, just her personal assistant and a publicist. It’s surprising to find such a huge celebrity in such understated circumstances, particularly given the intense scrutiny the Jackson family is under following the loss of its most famous member in June this year.

“People don’t really know, they don’t look in,” she says, staring back to the boulevard once more. “Nobody notices.” Brief respite, perhaps — since she appeared on stage with the Jackson 5 at the age of seven, all people have done is peer portentously at Janet Damita Jo Jackson’s professional and private life. “Certain aspects [of fame] aren’t easy, but I’ve been fortunate,” the 43-year-old says of life in front of the lens. “There are always paparazzi, but there are restaurants or places that they don’t know you frequent. And the people there are loyal, so they stay quiet.”

Unlike some of her siblings, Jackson knows about discretion. Since Michael’s death, she has been the quietest of the clan. Generally, despite a celebrated singing career that has ranged from the provocative to the political, she has kept her private life just that. Nobody knew she had married the choreographer René Elizondo in 1991 until they divorced in 2003. Her relationship with the producer Jermaine Dupri, which ended earlier this year, was also kept relatively clear of tabloid tittle-tattle.

“I think, to this day, people view me as a very shy person,” she says. “I don’t think I’m shy. I’m just quiet until I get to know you. I sit back and I watch and I observe. Though I’m someone that loves life, loves to have fun — I love being around my family. And I’m ambitious.”

Driven she absolutely is. Over the three decades of her recording career, she has reinvented herself almost as many times as Madonna. She has done political, playful, sensual, charitable and, following that infamous Super Bowl boob, controversial. Initially, however, she was little more than a pop puppet. “I was never really into the earlier stuff,” she remarks of the trite teenage albums Dream Street and Janet Jackson. “At that point, my mind was set on going to college, but I did music because it was what my father wanted me to do.”

A notorious disciplinarian, Joe Jackson was incredibly tough on his children. Janet has said in the past that the rigorous regimen was a double-edged sword: “Because of it, I’ve been able to achieve a lot of things that I wanted to. Granted, it took a lot of childhood away from me, but to have that focus has truly blessed me.” She wrote her first song at nine, appeared on the family variety show the same year and signed a recording deal at 14. She has never ridden the subway, and can’t go out for coffee, but she doesn’t seem regretful. “I can’t say I miss it, because I don’t experience it. And don’t get me wrong, I still get to enjoy it here and there.”

Jackson finally took charge of her career on her 1986 album Control, when she began writing, producing and playing keyboards. “My brothers took piano lessons when we were kids, so I wanted to take piano lessons. Then they quit because they went on tour, so I quit because I didn’t want to take them by myself. But that’s where it started from; I started playing by ear.”

If Control, with lyrics such as “When I was 17 I did what people told me/Did what my father said and let my mother mould me”, was about cutting the apron strings, 1989’s multiplatinum-seller Rhythm Nation 1814 saw Jackson develop a social conscience. “There was a major drug issue back then,” she recalls. “Crack cocaine was being introduced in the inner cities, and it was cheap. I remember seeing something on CNN about a little kid who was homeless, sleeping in the back of a car. And that was what it all sparked from.”

As well as politics, she has drawn inspiration from all manner of places: “I used to watch a lot of MGM movies, so Sammy Davis Jr.” She is also an unlikely fan of that mammary-mad British milkman Benny Hill. “I love [him]. When I was in school, I would watch it before going to sleep.” Later albums such as The Velvet Rope explored Jackson’s sexual side, a subject she continued to discuss as recently as her 2008 release, Discipline. Yet her new single, Make Me, recorded for her greatest-hits compilation, The Best, is simply about partying: “I think people want escapism right now, because there’s so much going on,” she says. “There’s so much heartache, there’s so much pain, there’s so much death. It’s a sad world right now.”

Although she might not be singing about it, Jackson is still in touch with her political side. “I think people are giving [Obama] really such a hard time. Everyone wants everything to turn around immediately. It took us how many years to get to this point? People say, ‘His first 100 days in office, what has he done?’ You can’t do that to the man. It’s not going to happen tomorrow. It’s going to take us time to get out of it.”

Having sold more than 100m albums, Jackson has had an impact on popular culture that shouldn’t be underestimated. This was a young black woman who wrote, produced and played much of her music, and whose cutting-edge choreography continues to inspire the newer generation of acts. Cheryl Cole’s recent X Factor performance tipped a military-clad nod towards Jackson’s Rhythm Nation iconography, while Britney Spears and Christina Aguilera have cited her as an inspiration. “She was one of the first female pop icons that I could relate to,” says Rihanna. “She was so vibrant, she had so much energy. She still has power. I’ve seen her on stage, and she can stand there for 20 minutes and have the whole arena scream at her. You have to love Janet.”

Jackson is appreciative of, if not fawning about, the flattery bestowed on her by today’s pop princesses. “I think it’s great for someone to emulate you,” she says slowly. “It lets you know that they’ve watched your work and admired what it is you’ve done.” For her part, Jackson “enjoys” Lady Gaga and “loves” Alicia Keys, for both her music and her spirit. “She has such a beautiful soul. I love her for that. There’s not a lot of them.”

Preparing to put herself back among the Rihannas and Gagas, Jackson is promoting The Best while preparing a European tour for 2010 and writing a book, True You, which, she says, will look at her struggles with weight gain and self-esteem. Yet for all her insecurities — she was quoted recently as saying that she hated her smile — Jackson seems strong. There’s no high-pitched simpering, no glibness, just steady, if occasionally guarded, opinion. It does, however, take time for her to be drawn on Michael. She finally opens up when pressed about her tribute performance at the MTV Video Music Awards in September. “It hit me before I was about to do the performance, and it hit me when we were in rehearsal. There was a huge image of him on this screen, and I started to cry. I had to step away.” She saw her brother two days before his death, and for months after avoided watching television, but his image is impossible to escape. “You know, a day doesn’t go by where you don’t think about him,” she says. “It’s always there, in every sense. “But it will get better. It’s not easy, but I know with time it will get easier.” She stops. “But it will never be easy. It’s my brother.”

Almost as soon as the M-word is mentioned, the PR machine kicks in, and Jackson must return to rehearsals. What motivates her to keep going? Surely she could sit back, admire the awards, the accolades, the achievements? “I think it’s just passion. That’s all it is. Would you do it for free, that’s the question. And if you’re passionate enough, you will. That’s what I think the secret to success is. You don’t want to stop, so, as long as you can, you keep going.” She pauses. “I hadn’t listened to any of the old stuff until we put this compilation together. The body of work trips me out, but I almost forget it’s there. I don’t look back, I just try to keep going.”