Amnesia in 19 year old after car accident

Setting: Modern day (2012-13) Australia.

I'm writing a novel which centres around of a young woman (around eighteen/nineteen years old) that loses her memory after a car accident. Ideally, I'd like her to forgot a lot of her life but judging from the research I've done I don't think that's entirely possible.

So I wanted to know how much of her life she'd forget before the accident if she had retrograde amnesia. Would it be possible for her to forget years of her life? Would she remember patches of her life before the accident or would it be possible for her to remember nothing? The research I've done points to her having other symtoms but would it be possible for her to be somewhat healthy other than the amnesia?

I've searched: retrograde amnesia, amnesia after trauma, fugue states, amnesia, psychogenic amnesia and I've read this post: http://little-details.livejournal.com/2082087.html


Thanks in advance