It's tricky to judge the true quality of a show when the audience is packed with a performer's friends and family, as I think was the case, but I don't know that for sure. Whoever they were, the audience loved the show and gave it a standing ovation.
Glennis has apparently not been on stage for a while and whatever nerves she may have had were deftly channelled into her performance. The premise is an interesting one and the writing serves it's purpose but, personally, I would have preferred a bit more depth in terms of exploring the reasons for her retreat into both the cave and musicals. I felt that there wasn't enough exploration of why she started drinking in the first place - it IS explained but I thought that the show could have done with at least one heartfelt ballad (since we're in a musical) explaining her true feelings/heartache - but maybe that's for Cave Girl 2.0?
That being said, I still recall one poignant quotable quote: "It's like suicide, without dying" which was one of those lines I thought 'damn, I wish I'd thought of that!'.
When the songs are in her comfortable range (a few require her to sing a little too low I felt) she has a stunning voice and there are some moments of great beauty. She has a masterful awareness of how to use her arms and hands whilst singing, that effortlessly compliment her emotions and the lyrics. She's a charismatic performer and instantly likable. It's an interesting mix of comedy and personal trauma.
Overall, I enjoyed it and I'm glad I saw it!