When his musician sister died from cystic fibrosis, Luke Martineau created an extraordinary memorial of her life to help other sufferers. By Clare Dwyer Hogg

Alice Martineau would not allow the word "brave" to be used to describe her. She hated it. It was up there with spiders on her list of dislikes. "I absolutely hate being called brave," she said in the BBC documentary, The Nine Lives of Alice Martineau, made about her last year. "I'm not." She looks at the camera straight on, steely eyed. "I'm not," she repeats. Throughout the programme, her brother Luke and her voice coach call her brave "just to annoy her".

Despite the mirth, there were very serious reasons why someone might have thought of describing Alice Martineau as such. She had cystic fibrosis - an illness diagnosed since birth, and a condition that was rapidly worsening. For those unaccustomed to the signs and symptoms of cystic fibrosis, outward appearances mean little. In the documentary, Alice, then 30, looks like a carefree young woman who's having fun. A part-time model, a graduate (with a first-class degree), and a Sony-signed musician with an album (Daydreams) under her belt, she speaks with confidence about her life and plans. With her large, cat-like eyes flickering with mischief, she talks about writing music, collaborating with the boy band Blue, and of how Robbie Williams came to her first gig. There doesn't seem to be any reason why she shouldn't achieve whatever she sets her mind to.

But appearances can be deceptive. Her eyes belie the truth. Invisible to the casual observer, her body is racked with pain, and pumped with a list of drugs longer than you'd think any body could take.

Her older brother Luke, a painter, features in the documentary, too. He knew first-hand what Alice was dealing with before she died in March last year. Because cystic fibrosis is a degenerative disease that attacks the lungs, Alice was permanently on oxygen: she had barely a quarter of her lung capacity because of multiple biopsies, and the parts of her lungs that were still intact were ravaged with infection.

"Grief is a strange thing," he says of the loss of his sister. "It can zap you between the eyes when you're listening to a piece of music, and you can feel overwhelmed, burst into tears and lose it completely. I watched the film about Alice last night for the first time since she died. I expected to find it hard, but I didn't find it as hard as I thought it would be. So you never quite know."

The Martineau family and Alice's friends have set up the Alice Martineau Appeal, in order to raise money for the Cystic Fibrosis Trust. Two thirds of the trust's funds go towards gene therapies which, one day, will ensure that sufferers enjoy a normal lifespan.

"Until now, the only way they've been able to treat cystic fibrosis is with antibiotics," says Luke, "just treating the symptoms. Now, they're developing drugs in mist form that you inhale. The mist contains healthy copies of the gene that is defective. The healthy gene copies itself into the lung temporarily, so that while you're dosed up with it, your lungs are healthy lungs."

He shakes his head, and we go upstairs, past children's toys and small socks (he and his wife have a toddler and a baby) and into his studio. It is filled with portraits of Alice - 26, to be precise. One for every letter in the alphabet, complete with a word that describes her. S is for Star. W is for Wins at Scrabble (a claim that Luke used to vehemently dispute with her). G is for Graceful (Luke's daughter is called Grace, so this one is particularly poignant for him). The paintings represent Luke's need to commemorate his sister's life force before it's too late.

"After Alice died, we had a big get-together with all her friends. Everyone was saying that we should do an appeal," he says. "We thought we could do a pop concert, but although Alice had achieved some amazing things, she wasn't Dido. We couldn't expect Bono and Elton to turn up." He grins. "That was really tough. I was getting frustrated and worried that we were running out of time. So I dropped everything and started to paint. I painted S - Star first, and worked for six weeks non-stop."

The paintings will be auctioned at a launch event today, which would have been Alice's 32nd birthday. "I'm going to miss some of these," he says, looking around. "There's a huge amount attached to this for me - it's Alice, and also it's my work. It couldn't be more about me, and my world, and my life, so it is kind of scary, really. It is quite loaded."

He is concerned lest people would think that the portraits are downbeat, or valedictory. "It's about celebrating Alice as someone who goes on in people's lives, being relevant - she's always going to be relevant," he says.

His favourite portrait is Q - Queen of Pop - which looks a little Warhol-esque. "As a whole, I want the show to feel iconographic. I think Alice has become, in a way, an icon. For anyone with cystic fibrosis, she is. I'm playing on that. And repeating the image, repeating the profile, just trying to ram it home. She was a steadfast character. Stubborn."

The sale will be presided over by a auctioneer from Sotheby's ("A professional auctioneer should get people bidding properly," Luke laughs), and among the guests will be Simon Cowell and the Duchess of York, who is a patron of the charity. "She chose us," he says. "Alice's boyfriend, Al, has a friend who was sitting next to the Duchess at some do, and they were chatting about Al's bereavement. She said, 'I want his number. I want to help him'." And she did.

"Luckily, Al didn't think it was a wind-up, because he's a real wind-up person," Luke laughs. "She wanted to do everything that she could to make Alice number one, to use her words. She genuinely cares. I think she's an emotional person, emotionally driven. When she says she wants to do something, she means it."

Luke finds the whole thing rather extraordinary. "I have imaginary chats with Alice a lot, and I say, look what you've done to my life!" In some ways, he's not that surprised. In her own lifetime, Alice did a lot of things that seemed entirely unlikely from the outset. A career in pop, for instance, isn't an easy route for anyone - notwithstanding breathing difficulties and severe illness. But, just like she wrote her songs to give plenty of space to take breaths, she fitted whatever she wanted to do into the rhythms that her body dictated.

The phone rings, and Luke breaks off from the conversation to answer it. It's Charlotte Walker, one of Alice's best friends, who is acting as treasurer for the appeal. Charlotte went to primary school with Alice, and used to hold her hand during sports-day races so that Alice, who clearly didn't have the lung capacity to run as fast as her peers, would never be last. She's calling to tell Luke that almost all of the 300 tickets have been sold.

Alice might be gone, but she has certainly left a legacy. And although she didn't like being described as brave, she didn't say anything about the word "inspirational".

For more information about the Alice Martineau Appeal and the Cystic Fibrosis Trust, consult www.cftrust.org.uk/aliceappeal