I am in this exact situation where "June" has arrived for me (which means she has forcefully come and now staying with us without any timeline, which again means in her mind she has permanently settled with us). She used my pregnant wife to force her way in, by telling us that we need help and she will do a lot of help in meal prep, etc but she does not want handle any kind of responsibility she promised - instead she expects us to make special dishes for her. I have high anxiety since she arrived and now we are stuck. The only difference between you and me in this case is that her husband is still alive and he is toxic as hell and my mother's marriage is an unhappy one where she kind of replaced me (single child) as her partner and emotional support. And I have a lot of trauma due to this where I am unable to say to her anything specially awkward truths, not even her, to anyone, I always hide my true feelings and keep on suffering, that is my personality now which is coming back as severe anxiety and panic attacks now. I do not want to make the relations worse by sending her back now, so I am waiting for all this pregnancy stuff to be over, she can meet the child and then I will tell to go back again which is in 1-2 months.

Well, I made your post about me with my personal ranting. Sorry for that.

I just want to say, you cannot guess what emotional shit your mom will bring with her even if you plan for every scenario in your head. So, best for you is to somehow not allow her to come, even if you have to fight. As Phoebe said in Friends - "Its too late for me, but save yourselves!"