She slips through the door resembling any other Gaza girl, head scarf and jilbab concealing her hair and body, and emerges three hours later looking like a beauty queen. But before Aya Abu Shoqa steps outside the salon in her wedding finery, she dons a hooded ivory satin cape, complete with opaque veil. The only men permitted to see the full picture – hair piled up and threaded with fake pearls, eyelids glistening pink and gold, a dusting of pale powder shimmering over her bare shoulders, her tiny waist accentuated by a diamante-encrusted bodice, satin cascading down to her stiletto silver sandals – are her new husband and her close male relatives.

The groom is the sole man at the 20-year-old's wedding party; even the photographer and videographer are women. A separate men's party is held beforehand, but Aya – as is the custom – is not invited.

There are dozens of weddings in Gaza each week, sometimes dozens a day. It's a matter of demographics: Gaza City has one of the highest population densities in the world, and most of its residents are under 25.

The crowding of 1.7 million people into a tiny strip of land shapes Gaza's image in the eyes of the world, and prompted David Cameron to describe it as a prison camp. Impoverished refugee camps, homes destroyed by military bulldozers or shells, wailing women, gun-toting men and traumatised children – all these help to build a bleak picture.

But there is also joy, love and family celebrations. Weddings are the core of Gazan social life. In a place with no bars, clubs, cinemas or theatres, a party is still a party.

Aya's transformation begins around 11am, behind the blacked-out windows of the Top Beauty Salon in a quiet street of Gaza City. Outside it's pouring with rain and a gale-force wind is whipping the Mediterranean, just a few hundred metres away. Inside, a warm fug is created by steaming water, blasting hairdryers, hot sweet Arabic coffee, the odd cigarette and a lot of female chatter.

Aya is already in her wedding dress; she cannot risk dislodging her elaborate coiffure or smudging her makeup by putting it on later. Her gown, rented for the day for a typical $400 (£250), is a little girl's dream of shimmering satin, sparkling stones, ruffles and flounces. A veil, satin gloves and costume jewellery complete the ensemble.

The hair-styling takes an hour; the makeup around the same. In between there are nails to be painted, earrings and a necklace to choose, friends and cousins to talk to, and excitement and anxiety to bubble up and be contained. The session in the salon costs around $80 (£50).

Aya tells me she was introduced to Bahar around six months ago by family members. The couple swiftly agreed to a marriage. Since then she has spent time in company with her husband-to-be, but today will be the first occasion he has seen her without a headscarf, and tonight will be the first time they are alone.

Does she love him? "Of course," she says. "He will be my husband." Is she nervous about married life? "I am scared about leaving my home and my parents, but I'm also excited," she replies.

Her mother Niveen says she is proud that her eldest daughter – there are four younger ones – is getting married. "It is a big moment," she says with a wide smile. I ask Niveen what she is wearing to the party; for now she has on her headscarf and jilbab. A long, black dress, she says, giving little indication of her stunning appearance later.

Niveen is 36. She got married at 15, and Aya was born the following year. It was normal, she says, but adds that she now disapproves of marriage at such a young age. Does she hope Aya will have a baby straight away? Inshallah, if God wills it, she replies. Aya quickly says she still has two years at university to complete.

The usual process of a Gaza marriage begins with family members of the prospective couple sounding out – and checking out – the other. If all is agreeable, the couple's fathers will negotiate a dowry. Later the parties go to court to sign a marriage contract and set a date for a formal wedding. From that point, they are legally bound to one another. A brief ceremony on the wedding day is attended only by the groom and his male relatives. Otherwise the wedding is marked with separate men's and women's parties.

Aya's party starts at 6pm. A red carpet leads to a stage, on which there is a canopied dual throne for the bride and groom. Arabic music pumps over the heads – covered and bare – of 200 or so women. Aya is literally centre-stage, dancing almost non-stop for four hours, sometimes with Bahar, often with other women: her mother, mother-in-law; friends and cousins. She is effortlessly graceful and sensuous; Bahar looks a happy man.

Niveen is in her element. Black satin shows off her still-youthful figure; her head is covered in black lace. She greets guests, fetches chairs, fusses over her younger daughters, all the time shooting reassuring smiles and glances at the bride. But it's a moment of mixed emotion: pride and relief that her eldest child is married, coupled with a sense of loss as Aya now becomes the daughter of her husband's family.

This, Niveen tells me, is the day that young Gazan girls dream of and older women reminisce about. In another hour or two, the guests will have departed, Aya's makeup removed, the hairspray washed out, the dress ready to return to the hire shop. The wedding will be over, and Aya's new life as a married woman will begin.