What is the next step from here?

I think she is just being friendly with you, and probably flirting with you, the point is, she is in a relationship. So you can't invite someone out who is in a relationship, even if you justify it and say it's just for friendships sake, you know its not, you want something more from this girl.You might be scaring her off also, she might be creeped out, so best to leave her alone first. If she wants to keep communicating,she will start communicating again