Parent of HS freshman girl so we've just done the whole middle school thing.
If your DD and her group are already seated when someone else says to move, they need to stay put. They're already there. They can look up and say, "No, we were already here" and turn back to each other to talk and ignore anything else that gets said by the mean girls.
I would not get involved as the parent here, but I would definitely keep the channels of communication wide open with your daughter so she will let you know freely if this escalates. It's the lunchroom for right now and they can manage it by just not sitting with these girls and/or by simply saying "We were already here" when told to move.
You do need to stay in the loop to be sure that this doesn't spill over into other aspects of school, especially academic classes where kids need to be focused on the work, not on drama. And just be aware that gym class and/or free periods like study hall types of times (many middle schools have them in our area) are the times when this crud might flare up in other forms. Just talk to your kid a lot but don't press her with lots of questions about this dynamic.
I think it is good that you as a parent already have the school counselor option on your radar, even though I wouldn't use that option for this situation. So many parents seem to forget the existence of the counselors and that's a pity, because they can be very helpful. This isn't a case where the counselor would necessarily be directly involved -- the counselor likely would not go into the cafeteria and tell the alpha-girls to cut it out -- but the counselor would be more likely to talk with your daughter about how to respond to such treatment. If things really escalate or if your daughter seems inordinately upset by this to the point it's a distraction, she could see the counselor for tips on how to react, but she, not you, should be the one to see the counselor if that happens.
In our MS, there were four periods of lunch, and the lunch period a kid had changed periodically from quarter to quarter so they weren't always in the same lunch period all year long. Does that happen at your school? If so, that can help defuse the problem as well simply because the same group of kids won't be in the lunchroom at the same time all year long.