Obviously it's going to depend more on your girlfriend than anything.

I started my wife on an EasyStar. She's now flying an LT-40 and I'm putting together a Dragon Lady and a kit-bashed 4-star for her.

Does your girlfriend mind the noise and mess of the glow engines, or is that not an issue? If she's strong on the simulator, I'd go with a .40 or .60 size glow trainer. You can alwasy "borrow" an engine from one of your existing planes. (and if she digs it, you now have an excuse for a new engine).

Oh, we used a Dx7 for a buddy box with my 72Mhz 9303 with no problems, so you won't have any trouble there, they work either way, as long as the master TX and the RX work together, the buddy box can be either 72Mhz or 2.4Ghz