When she's really ready to be done she'll be there - but be ready for it to be heart wrenching for her (if she's an adolescent then). DD was probably "ready" a year ago, in some ways, when she lost her coach and had to try a new gym that really didn't work well for her socially or coaching style, but she came back and trained another 6 months because she "loves gymnastics". Again hit a wall with the difficult team mates and coaching style, pushed through a couple of months of being very unhappy there while getting all her old skills back and multiple new ones...then had to take time off for a new school, and hasn't wanted to go back. She's finding new things, cheer is letting her still do "some gymnastics" and although she really misses bars and vault (not beam, although she was an amazing beam worker, because of fears that had been thrown in her face for a year), she no longer feels bad about herself for 20 hours a week..
I will say that she never mentionned wanting to quit until her coach left last summer - through a year of L7 with tons of success and being ready to move to L8 with the anticipation of continuing to succeed (she was 11) - but she now tells me she thought about it often - and it was the way she was coached and the great social environment of her previous gym that helped her through those times. I mention this because once those 2 things were gone, there was nothing I could do to keep her in gym - she did her best to be sure she was ready, and that it wasn't that she couldn't do things, or was too scared to try, etc. In the end it wasn't fun anymore and the postitives were gone (no longer built confidence, friendships, team spirit, etc) - had they still been there for my kid, she'd still love being a competitive gymnast - but they are all done sometime!