(DG posted while I was composing this - don't think it disagrees, I am naturally less direct!)
Am passing on info gained from friends rather than direct experience -
vet school seems to be more competitive than even medicine
I can't provide evidence that getting a B grade will exclude her from selection but I know of children with A* at GCSE and A/A* at A2 that took two attempts to get a place and several who only got one offer from all their applications (they also had masses of relevant work experience)
There must be a danger that faced with many really strong applications the admissions officers will be looking for ways to cull and it could get down to B grades at GCSE. I know that at 'our' highly selective GS the Oxbridge, Med/Vet applicants would not be expected to get B grades at GCSE.
I do know that for medicine there are Universities that reject those who don't have a certain number of A/A* grades so in that sense the B grades don't necessarily exclude but you need sufficient to compensate.
At the risk of causing offence my honest opinion is that it is a hard slog to get the grades and experience required for entry and your daughter will need to put in a lot of effort. Year 8 is still very young to take on the weight of this but it might be a good thing for her to realise that if she wants to get to vet school ( and indeed get through the training) that she will need to work really hard and probably have to overcome various difficulties.
Your comment that she could do better therefore seems perhaps to be the man issue.
Maybe a chat so that she starts to realise how much commitment is needed and sorting out the MFL that she has to take at GCSE could be a start?
Concern about moving to a class where she fears being bullied must be awful but if the child in question is allowed to bully others within lessons then contact with the school is certainly called for!
There is quite a lot of online material that you could encourage her to use over the summer. I haven't used my French since O level so didn't feel up to it myself but if you are reasonably competent then the standard isn't that high!
I have used a tutor for all my DCs, who although bright have struggled with MFL and had to work hard to avoid the B grade. The main element this provided was confidence and was well worth the investment not only for the exam result but in overcoming the belief that they 'couldn't do French'.
It depends on whether your DD is at a selective school but I can quote several children who have achieved A/A* grades from lower sets at 'our' GS so she might be able to achieve without moving sets?
There is plenty of info on the internet about vet school applications -
these might be a good start if you haven't already seen them - https://www.rcvs.org.uk/education/i-want-to-be-a-vet/http://www.rvc.ac.uk/Undergraduate/Index.cfm
you may already be aware but the course in the UK (unless I am out of date!) are only
Glasgow, Edinburgh, Liverpool, Bristol, Cambridge, Nottingham and London.
so its relatively easy to check each web site for entry requirements (grades and experience).
Worth noting though that the 'minimum requirements' will be essential but probably not sufficient!
Last! thought - does the school have a 6th form 'vet society'? Maybe they could find a sixth former who has got an offer this year/is about to apply who would talk to your DD. Sometimes teenagers take more notice of each other (or maybe that's just mine
Its great that your DD already has a goal to work towards - mine were much older before they settled on anything (very last minute in one case and one still not sure!) Hope she gets on well.