Right. There can only be 1.0 difference between partners in mixed (in our league).
She can appeal up to 3.0 and be eligible. Still, if you are worried about her being frustrated, 7.0 mixed is probably not a great plan. In fact, it is probably the worst possible plan.
When I first played 7.0 mixed as a 3.0, I felt as though I had landed in some new tennis universe. I couldn't return the serves. I couldn't return the groundstrokes. The serve that won me so many free points in 3.0 ladies was getting crushed back at me. People took the net and pinned me in the back corner. Guys hit twist serves and topspin moonballs that I was helpless to handle because I couldn't hit on the rise.
Why put your wife through that now?
-- Random Error Generator, Version 4.0
-- Master Moonballer