sister in-law visiting

So we are pregnant with our 3rd child I'm gonna be 19 in December yes I know 3kids at 19 lots a people judge but on the other hand she has a child who is 4 an she's coming to visit. shes staying a week an every time she comes down her child is an asshole to my almost 2year old an we constantly get into it she claims he has mental health issues but that's not the case as her mom raised her son up until he was 2 years old an I was around him an took him to all of his appointments. I've said I do not want her here bc she will not correct her child an I'm constantly stressed when she's here an I'm high risk as I have a past of delivery extremely early. my husband said that I have no choice he pays the bills so I said I was packing me an the kids an leaving until she was gone. it caused a huge fight...am I wrong for feeling like I need to leave to protect my child from hers? btw my husband won't say anything to her when her kid is mean to ours.