"She mentioned that she still wanted to go over and watch the band but she stayed put. I took a stab at failure and left her alone with the other guy at the bar"

The author did a good job and it worked out well! But in this scenario (where it is likely she's interested), be confident, stand up from your barstool, nod your head toward the band, and ask her to join you with a smile!

Otherwise you run the risk of letting her think that you aren't interested. And, confidence is kinda sexy ;-)