I would say search out a used-but-like new Berretta 390/391/3901. I saw an LNIB 390 20 ga at a pawnshop for $389, a smokin' deal. Cabellas often has like-new trade-ins.
Also a Franchi would work if you can find it. Yes, I know, she wants a 12 ga, for her frame I think a 20 ga AL48 would fit, though it is a recoil op'ed gunn
Tri-Star sells SA guns in the price range.
Has a Browning Gold, $600, used. A couple of Verona field guns for $400, $250. A Beretta 390 Gold, $550, very good deal; you better buy it before I do!
Have some fun, browse Jaquas for a spell.
Oh, that B 390 Gold has 24 inch barrel. Looks like it might be a winner.