Jaime Winstone was very badly cast. She looked a good ten years older than the role demanded and was huge in stature in comparison. Her prominent jaw doesn't lend well to that role either.
I felt sorry for her, because she's probably a good actress, but the casting was shite.
It didn't help that the wigs were totally unconvincing either.
Samantha Spiro was spot on.
It's a shame that the character of her mother wasn't developed more. Was she a pushy, stage mum? Was she struggling as a single parent? Were there any other children?