And to go back to the original question... Yes, she is probably gifted. This doesn't change her, this doesn't make her into a freak. Unless you need ammunition you don't even need her to get tested (which might require somebody experienced with older gifted kids) unless the school requires it for the acceleration they don't seem loath to offer (which might be good).
Gifted is IMO a label you can start (privately) applying to her and and using to find help for her, starting with online resources such as Hoagies or this forum. Lots of people here have been there, done that, a few in the UK.
+1 on everything kcab said about things needing to change soon. What are your options? Working with this school, other schools (public -- in the non-UK sense of the word -- or private), homeschooling for a while, extra-curricular course of study in her areas of interest while rekindling her love for the basics -- if she likes chemistry she will need math!
