Head of Year 7 here: very normal so please don't worry too much. However, it is unpleasant and can really knock the confidence of some children.
My best advice, having seen this a dozen times a year, is to really encourage your daughter to make lots of new acquaintances/ friends. Any extra curricular stuff available is great to join in with: sports, art clubs, science clubs, creative writing, drama etc. A variety of different students attend these activities, away from their usual 'friendship groups' and it can be a great way to broaden her horizon and make friends with like minded people so that she's not having to rely on these two friends, who don't sound very pleasant.
Also, definitely continue to monitor her social media and block and delete anyone making nasty comments. There is very little the school can do about this as it is the parents' responsibility to safeguard their children outside of school hours, when I would imagine these comments are being sent/ received. Remember that legally, she shouldn't really have access to social media at all until she's 13 so it really is up to you to safeguard her mental health in this regard. If things become extreme, you should report to the police.
Inform the school but don't expect them to take action as it's really not their responsibility. You could also have a chat with her form tutor or head of year regarding how she's been feeling regarding friendships as they may be able to step in gently and manufacture a few positive friendships, if that is needed further down the line.