I don't think it would be a problem. Avis lets a "life partner" (same address on DL) drive your car, so you'd have to show both DL to prove you meet that criteria. However, why not just book 1 in her name and 1 in your name? You should be able to get the same price with/without your name (just use the same AWD/coupon). When you get there, you can always ask for upgrades if they don't automatically give them.