I agree with you and yes, email the teacher and voice your concerns. Your dd doesn't need to be a doormat and deserves respect. The teacher will also be better placed to support what sounds like a vulnerable young lady if she has insight into the harm she's doing to her friendships.
DD2 is 11, and is in her first year of senior school. It is a school with a junior and senior part, and she also attended the junior school. Several of her junior school friends are in her form at school.
She has one particular friend, who has been her "best friend" for a long time, but they often fall out, and (I realise i am only hearing one side of the story) it sounds like this friend sometimes uses her as an emotional punchbag. For example, she was once "accidentally" horrible to DD2 when she was upset with her mother. Also, last year, her mother had serious health problems (now resolved) and she (the friend) was very nasty to DD2 at that time. The nastiness takes the form of ignoring DD2, spreading tales to DD2's other friends, to try to get them to ignore her; that is, psychological rather than physical.
After a while, she will apologise, and all will be well, but then it will start up again in a few days or weeks time.
So, DD2 had decided that the next time she apologised, she would be friendly to her, but not be "best friends" anymore. I think this is wise, as, even if DD2 is partly to blame for the arguments, it doesn't sound like it is a healthy friendship, anymore. DD explained this to her friend, when she apologised.
All well and good, except the form teacher has now got involved, and said that as this friend has apologised, DD2 should accept that, and be her friend.
I think that there is a difference between forgiveness, and being a doormat. DD2 should accept the apology, but not have to hang around waiting for the nastiness to start up again, only to have to accept yet another apology. I don't want her to get the impression that she should put up with being treated like dirt in any relationship, just to keep the peace.
I have suggested I email the teacher, but DD2 does not want me to.