There is no competitive league anywhere for a 2.0 player, so far as I know. How does it make sense for her to rate as a 2.0?
Around here, playing opportunities for 2.5s are rare. I think the sensible thing is for your wife to rate as a 3.0. If she is hitting with you regularly, she probably would be fine at 3.0.
I would say that if she cannot hold her own at 7.0 mixed with you at her side, then she probably should hold off on playing mixed for now. She could cut her teeth on 3.0 ladies and then try mixed.
Still, I suspect she is stronger than you give her credit. I mean, have you seen the bottom of 2.5 level? Surely she is stronger than that.
BTW, if you are "dumbing down" your own play to participate in this league, you are probably sandbagging. Are you a computer-rated 4.0 (what does "officially" a 4.0 mean?)?
If not, I would suggest you and your wife bag this idea of playing mixed together. It's not fair to the opponents to have a male opponent who is sandbagging and a female opponent who shouldn't even be out there.
I do have an idea for you, though. When I was a 3.0, there were a couple of guys who coached ladies teams because their wives or girlfriends were that level. It actually worked pretty well. The guys got to participate in tennis with their ladies without partnering with them. The wives/GFs were more apt to listen to advice because it was offered by the guy during practice rather than in a competitive setting.
Maybe you and your wife could form a new 5.5. combo team with you as coach? Or you could form a 6.0 mixed team and coach it and not play?
-- Random Error Generator, Version 4.0
-- Master Moonballer