NTA. If anything, your teacher is TA for moving her out of the group after she had already worked on quite a bit of the project. It would be slightly different if she had been moved within the first day or two, before any work was done, but in moving her after a considerable amount of work was done they not only didn't give her credit for the work she had done in your group, but created this conflict. Since you and your group have already put in a significant amount of work it wouldn't make sense to give her group the idea and force you all to start over, and your group members are right to be angry about that- I wouldn't bring it up again. Her wanting back in to the group just seems like she's frustrated about the situation and lashing out a little, and she's right to be angry, but she shouldn't be angry at you. Instead, I would see if you could email your teacher along with your group and explain that you've already done a majority of the project, and that your sister has put in a lot of work on your project, and see if they'll switch her back in. The advantage that the two of you get by living together seems minimal at best since you do have other group members that you need to work and communicate with, and the teacher might see that moving her is causing more harm than good.