I hear there's decent money in it.
I don't train my guy but we do train together and compete together. It's easy for us because we have the same goal in the same sport; it's more parallel training than one person training another.
Like someone else suggested, point her in the right direction and give guidance as necessary. Personally, I think setting yourself up in the 'teacher/leader' role in a romantic relationship doesn't really work well.
When things go for a shit consult the marriage counselor above.