This, it wouldn't be a good idea if it was so soon, and the ex was still sore about you but it sounds like everyone has moved on.(Original post by maskofsanity)
I don't see the big deal.
It was over a year ago, she's had a boyfriend, the other sister likes you, and they have obviously already spoken about you. Sounds to me like the first sister doesn't care...
Give it a go, and if need be you and her sister should talk to her and let her know how you feel about each other.
But yeah doesn't sound like an issue.
It's 2013, big girls don't need to get all hung-up over a brief fling.
Does anyone use their degree?