Two old, epic sayings come to mind:
"Bros before hos"
and
"All's fair in love and war"
So really, it's up to you to decide if blowing off your buddy is worth it. From my standpoint, when I played music and someone told me they would come to my show, I never fully believed them until I actually saw them there. I know I sometimes tell people when they ask that I'll come see their band but things sometimes come up in between and I have to blow them off. I expect the same happens to others as well. No big deal, unless I swore up and down that I was going to come, I wouldn't feel guilty about not going.
How long ago did you meet her? If it was like the last week or so, I wouldn't get into the birthday shit right away. Maybe tell her Happy Birthday and possibly a card. Or you could offer to take her out for dinner maybe.
As for what her signs could mean... fuckin' good luck with figuring that one out