My suggestion for the perfect amp for your girlfriend is a nice integrated triode tube amp with MANUAL BIAS. The more power tubes you can get away with the better. Hear me out because there's a method to my madness.
Buy her the integrated you want and over time build a nice system around it. On her nickel, of course. If things work out between you as a couple, you will always be around to maintain the bias on her amp and she'll appreciate you for it. She will love the sound it makes and you will get to play audiophile at HER HOUSE *anytime* you want! Just remember to NOT overdo it.
Should things progress to a mixing of, pardon the phrase, each others equipment, you will have a good start on a nice second or (ahem) bedroom system. You might even be terribly lucky and convert her to "audiophilian" by spoiling her with beautiful music. Even without her consent.
On the other hand, and this might sting a bit, but the odds are that if the wheels do come off for you there's going to be a "next guy". Assuming he'll be at least smart enough to learn how to set the bias on the amp, you know he'll eventually hook up a pair of inefficient speakers with 2 ohm dips. The sound quality will degrade fairly quickly and she will get what she deserves. Weak, hollow, lifeless music in her life because she picked the wrong guy.