My niece got a waver like this on the Fantasy last August. She was 13 and a half (so not particularly close to 14), but we took her up there on the first day with her sister and two cousins (my sons) who were all Vibe age. The CMs gave her mother the waiver to sign, no problem. YMMV. She did spend some time in Edge with my 14 YO son who could do both, but she enjoyed being in Vibe. She says that didn't feel bullied or pressured by the older kids, but it probably helped to have three people she knew already. She is a little on the shy side, so I think this was a great opportunity for her to build confidence. The CMs are great and they do a good job involving people and keeping a good atmosphere of inclusion.
Since your daughter has done Edge before, you might already know this, but I was surprised how late Vibe activities run. (They have a better night life than the adults!) Her parents chose to have her come home sooner than the 2AM that some of the activities ran until.