My twelve-year-old wants to convert to a different religion. Is it a good idea, and how should I support her?

My twelve-year-old daughter wants to convert to Catholicism. She's been doing some independent studies on the religion, and she wants to convert. I don't really know if it's a good idea or not, because she's young. Has any parents ever gone through this? I'd like to know how you helped your child convert to a different religion.