MIL driving me insane!!!

(We live with my MIL) So a few days me and my son were walking our dog, my husbands 2 kids were over this weekend and she decided she wanted to tag along too bringing my MiL along, wouldn't be a problem.... But she left the 7 month old alone in the house during this walk!! Well fast forward to today she had my son and my oldest step daughter outside playing while I went upstairs to give the 7 month old a bath, I heard her bring my step daughter inside and I looked outside and she left my son who is only 4 alone outside with no one out there!!! We've been looking for our own place and now I hope it happens quicker cause I can not stand this anymore! Who in their right mind leaves little kids all alone to carter to ONE kid when there's 2 more??? I'm 24 weeks pregnant I can not be dealing with all this stress when she already causes me a ton of it