My fiancée and I have lived together for over 3 years. We do not have a signed Domestic Partnership. 2 months ago she unexpectedly slipped into a coma.
Her father, who she had a very strained relationship with, now suddenly has POA pertaining to her medical decisions.
You aren't married. In 3 years of living together you did nothing to document your arrangement, whatever you want to call it. That makes you roommates, in the eyes of the law, not family.
It sounds like she didn't have you on her HIPAA authorization forms, probably because there weren't any current valid authorizations on file with her health care providers when she lapsed into a coma. In the absence of this, family trumps roommate.
The $ cheap way to see your partner is to get her Dad to take you off the excluded list. Of course, don't hope for this if you are seen as responsible for putting her into a coma. (Not saying you did, but over the internet I can't tell your character.) If Dad just doesn't approve of your relationship for stupid reasons (e.g. race or sexuality), I could see why you are at an impasse.
If you have access to her health care information, gather any information that you can find about her prior authorizations. In particular, look for items where she put you on her list of people authorized to see her medical info or emergency contact. Bonus is if you can find documents where she explicitly excluded her dad, if any exist. Have a list of this info available when consulting with a lawyer.