The Catholic religion is traditionally a lot stricter than other branches of Christianity, but that isn't necessarily the case for all Catholics.
I would say that the biggest issue would not be that she believes in God, but more her beliefs on other issues. How does her religion affect the way that she thinks about say, homosexuality? Or contraception? (I know you said sex isn't an issue now, but it might be down the line, and one of the stricter Catholic beliefs is you can't use contraception).
I used to go to a youth Bible study group. I wasn't very religious, I didn't go to church usually, but it was my friend's church and I was mostly there for the support we gave to various charities. I stopped going, however, after some of my friends said in no uncertain terms that they thought anyone who was a non-Christian would go to hell. I thought it didn't make sense that you could accept different sexualities, different races, different genders, but you couldn't accept someone who was a good person, but just didn't believe the same things as you.
So as long as your fundamental beliefs don't interfere with each other, then I think you could really work out. Maybe she helps out a church because she enjoys helping people and that's something everyone can agree on
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