The guitar thing is definitely your "in" (literally and figuratively).
Get up behind her, place her hands on the strings real gentlelike. Teach her how to place sweet music. Make sweet music for her. Look her in the eyes and play something sexy. Make sure she knows it's for her. Make sure your pants are off already. That way she knows you mean buisness.
But keep your socks on, your distance runner feet might turn her off. Also, make sure they're buisness socks. That way she definitely knows you mean buisness. Play something sexy like wonderwall or crazy train.
Teach her the A string, the B string and the C string, all the way to the E string. This will get you to the most important string of all, the F string. Make her hand, guided by yours, play beautiful music. Brush her cheek with your lips. Caress her hips with your hands from behind.
Give her a look of passion, play her a love song (in spanish, italian, french or any foreign language really, if possible. If you don't know any foreign songs make shit up) then be cold and give her terse answers and look away for 60-90 seconds. Repeat in intervals till she tosses the guitar aside and jumps your bones.
Or use the D.E.N.N.I.S. method. Your call.