It's an awesome story and if you don't mind spoilers I'll tell you:
Basically, she goes to faerie, ends up pissing off Titania (which, to be honest, wasn't hard) and her hatred (and I think her slight mental illness if I remember correctly) makes it such that anything she touches bursts into flames. She ends up confronting Titania, who finally apologizes, but Molly accidentally eats some fruit. Titania sends her back to earth, but she is not able to touch the ground or eat/drink anything. Tim (being the oblivious kid that he is) doesn't notice, and Molly gets upset at him and leaves off to places unknown.
I don't remember anything after that. I think that's where the Books of faerie pick up, and I don't remember if I read those.
Of course a whole lot of stuff happens while this is going on (Tim hangs out with one of the old rulers of Faerie, Hell comes to collect the Tithe, etc.)
The Books of Magic are and always will be one of my favorite comic series of all time and I'm happy to spread the love. I should scan some of the issues I have (I have every issue not collected in trade).