That's nice, I mean if your girlfriend really loves you, she should.
About hair, I want to first tell you, that neither all ladies look good in haircuts, nor long hair look bad on all. It depends upon person to person, but yes - styled hair - for which the use of scissors can play a critical role, surely look good, nice, lovely, beauteous and attractive, rather tempting. You should suggest a cut, by looking at her face, its structure, her age, her colour-complexion, her job, her nature, and many other things. For example, for a chubby, round face, with fair complexion, the pixie cut, or a cut in which hair hang around, like bob cut will work wonders. She will look cuter. If her face is longer, shoulder cut will do, but - what if she prefers long hair... in that case, ask her to get her hair straightened and trimmed, from ends.
Take some cues from here -
http://www.ukhairdressers.com/hair_move/
Tell me her facial structure, and I shall try to help, if I can.