At the end of the day, I don't think you should be judging the singer's motives, whether the gig is good for THEM or not or whether it's right for them to do the gig. You book based on whether they'll pull an audience and that audience will enjoy them.

That said, I've listened to part of a song (slow connection), and I don't think she's a headliner. She's good and will get better, but I think she needs more time and experience. Know that I'm not 100% convinced I'm right.