I think she does remember that she heard George’s voice before the accident and was trying to tell them that in the car on the way home after she left the police station, but Kate started talking over her. This from the synopsis…
Alice starts to recount what she does remember. She was in a lay-by on the lane by Heydon Woods, where she has gone before, and she turned the car off and put the keys in the glove box so she wouldn't accidentally... She remembers hearing George's voice...
Kate assumes that was when he was checking on her after the accident, and did most of the rescuing: they have an awful lot to thank George Grundy for.
That is not what Alice means: he was... the car was off... She just wanted to be alone, she didn't want to hurt anyone, and wasn't planning on coming back until it was all done with.
When Kate asks what was done with, she impatiently says 'the vodka' and adds 'my anger'. She wanted to get it all out of her system, and then when she was clear again she would have headed back. Still wearily, Kate asks if she couldn't just have had a drink at home, at which Brian expostulates, but Kate, the practical, tells him it would have been safer, that's all.
Alice angrily says that home was otherwise engaged, and Brian intervenes: they must have told her at the station that when George and Alistair found her, she was in the car, on the bridge, the bottle she bought from the shop was empty and she was pretty-much out for the count.
Alice mutters that is not what she remembers, but Kate firmly informs her that it's what Alistair and George remember, and they weren't drunk to the point of unconsciousness. Brian intervenes to suggest they might have some quiet time for the rest of the journey.