Fountain of Knowledge

First of all, and totally on a different subject, thanks for everyone answering my coffee shop/high school question. that's exactly what I needed to know

Here's my new question for the day, it's about Amnesia, and I'm looking to get a little technical. I looked it up on Wiki, and it says that short term amnesia assocated with psychological trauma is possible, but not nearly as common as TV and movies make it seem.

From what I've read though, it sounds like what I need my character to do is medically possible. Kenz is a twin and watched her sister, Maddy die in front of her, and also (possibly) suffered physical injuries of her own at the same time. When she wakes up in the hospital, she has enough gaps in her memory that she believes her mother when the older woman says Kenz is her Maddy instead of herself. She vaguely remembers friends and events, although she's confused about why she remembers Kenz's life better than what she's told is her own. And this doubt, combined with a stark shared memory with an old friend, brings her memory back.

Does anyone think that sounds unbelievable/improbable? Amnesia isn't necessary for this plot line, but it would help at least in the begining.