Okay, here's what you need to need to know: This is Spider-Girl and we have made her better, stronger, faster -- older! And retired, actually, until a certain insect-themed crimelord decided to kidnap her baby brother. The kid was saved, but poor Spidey got stuck in the nexus.
As for why she hung up the webs...you could say she learned the hard way that you don't deserve great power if you don't have great responsibility. Of course, we all know this isn't gonna last long.