I landed up dating and loving the first and only woman of my life about 18 months ago. She was not skinny, and not that pretty. I'd never been into women either. We just started as friends who cared, but not long afterwards, the feelings became more romantic. It definitely wasn't just sexual.
I truely believe that attraction goes much more far reaching than just looks. If you feel yourself attracted to her, but she isn't physically what you would normally go for, I think you can safely assume that these feelings are a lot deeper and a lot more genuine.
I'd really not miss out on the opportunity to discuss these feelings with her....