Well, we always say that if you dont want to be friends, decline the invitations, and that's what you did. We also say stop giving the invitations and take the hint if they've been declined a few times, and it sounds like that's what she did.
So this is really just natural consequences of the situation, imo.
If you want the friendly relationship back, I'd make an overture - an invitation to coffee, to meet outside for a few, bring over some food or something, let her know about a neighborhood jewel, etc. Or, if you really dont have the time, then just continue being friendly and engaging her in a chat every so often, but dont provide any invitations. But I'd say you can't really have it both ways, kwim?