I'd talk to it first and find out what it's about. If it's just a spirit possessing the doll, I'd try and convince it to inhabit a cooler toy, like a G1 Transformer or a Mr. T doll, then I wouldn't mind it so much and we could probably get up to some lulz (especially once I show it The A-Team and it learns to talk like Mr. T too, or if it inhabits a G1 Transformer, I'd convince it to haunt Michael Bay, sceaming "Michaeeeeel Baaaaay! You raped meeeeee!")
If however, it's a evil creepy doll and will always be a evil creepy doll, then I'd have to ask it to leave or destroy it. It would be embarrassing having a girl's toy following you around, 'falling' out of your bag in public and appearing in your room when you have company.
If I knew for a fact it was evil, then I'd get in contact with my local Exorcist (every Catholic Dioceses has one) and take whatever course of action he suggests.