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My son is a barter and is sick again. He is 7. Finally getting fluids into him and so on. I just told his mom as she was away this weekend on a work retreat. She says she is coming over as soon as she lands. Well. It is my week and I have the situation under control. He hasn't even asked for her. She is a great mom, but this is over stepping boundaries. Nothing is written up legally, but I am doing fine, and my son I believe is recovering. He is holding fluids down right now. It is my week, and I will ask for her help when I need it. We have been a part for a few months.
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I encourage you to set boundaries. If you are no longer living in the same home, then you have the right to set a boundary regarding when she is welcome to come over. If you have agreed to a schedule of when you have the kids, you can enforce a boundary and tell her that is will not be taking the child with her.
I think you are doing this. But I want to re-enforce that you are doing the right thing and you have every right to do it.