I haven't read the whole thread, but would like to tell you my perspective. We live in Kent, that also has grammar schools. We are very lucky in that there is also a very good "comprehensive" (I say that, as most of the top DC have gone to the grammars, so comprehensive is a misnomer) that we are in catchment for.
DD was a bit like your DD. Primary was "feeder" for comprehensive, but grammar is girls only and she has had her problems with that sometimes. She did go to the comprehensive (along with our other two DC) and was in top set for most of her subjects (apart from English, where she was in Set 2 or 3, but that made no difference at all to her GCSE result, as the teacher was fantastic - she got an A).
She decided that, after being at the primary with the same people and the comp, too, she would change 6th form. She has done that with no problems. It is her first day today, so we shall see how she has fared.
What I'm trying to say is, if your DD is capable, going to a comp will be no problem for her if the comp is good. Around here some of the grammars are not renowned for their pastoral care, which is a big thing, I think. They are only concerned with their results and figures.
Only you and she can decide which school is best for her, but she can always change, anyway, at 6th form if not before.
Btw DSs had/have a completely different school experience to DD, so it definitely depends on the DC.