Rokhsareh Ghaemmaghami’s delightful documentary about a determined, resourceful Afghan girl who dreams of being a rapper tells us plenty about the trials of being a woman in the most aggressively patriarchal societies.

Living as an undocumented exile in Tehran, 16-year-old Sonita Alizadeh is at risk of being sold (that word is used frequently) to a potential husband back in the home country. She may fantasise about having Rihanna and Michael Jackson as parents, but her rhymes are drawn from her desperate everyday realities. No blag. No bling.

Sonita put together Brides for Sale, now a YouTube hit, as her mother was negotiating for a $9,000 dowry from the family of an older man. Sonita and her friends walk around with virtual price tags on their head.

The teenager proves to be an ideal subject for a film-maker. Articulate and stubborn, she has the courage to press older women on the injustice of the arranged marriage. “It’s our way” they reply vacantly.

It is also their way to prohibit women from singing for anybody apart from their husbands. Early tension derives from concerns that Sonita may never make her escape.

About halfway through, the picture takes a swerve that pushes us into tricky, self-conscious territory. The boom operator imposes himself in a conversation Ghaemmaghami is having about paying Sonita’s mum to delay any potential marriage. The director then points the young rapper towards a scholarship at a college in the United States. The narrative gets tenser still as the heroine travels home to secure a passport and arrange a travel visa.

Documentary purists may balk at the way the film-maker allows herself to become part of the conversation. In fact, she does more than that. Ghaemmaghami’s intervention makes a conventional story arc – remote possibilities leading to remarkable triumph – considerably more likely than it would otherwise have been.

The truth is, however, all up there on the screen. It would be mean to complain too volubly. A delight.