Yes it could turn out to be a very good thing for both of you. If she relapses it is because of her, not you. She could never relapse, or she could relapse once a year every year until she dies...who knows?
I think the bigger concern would be can you live a life with an RA? It comes with its own set of problems.
Three years under her belt is awesome. And there's something to be said for taking things slowly.
Good luck!
~T