I agree that you should tell your boyfriend that due to Covid you don't want to have her come for a visit. Her being in college has exposed her to different people and right now it's just not safe for either you or your boyfriend to have her visit.

You mentioned that your boyfriend divorced her mother 10 years ago and it sounds like his daughter carries a lot of resentments and that this is probably also fueled by her mother. This is something your finace has to deal with and you have every right to not want her negativity in your home. This started when his daughter was only 11 years old. He needs to have a serious sit down with her.