Mama bear is coming out

So my sister in law and I don’t get along. It’s an unspoken hatred. our kids are only 3 weeks apart in age. Every Sunday we go to dinner at my mother in laws. So when my son was 2 weeks old he was hospitalized with meningitis then at 4 weeks old he was hospitalized again with RSV. He is now 5 months and still having respiratory issues from the RSV. Two weeks after he got out of the hospital the second time I had asked my mother in law in the family group chat to watch him for awhile while my husband and I went to Walmart since we didn’t want to take our son and expose him to anything. Upon our return from shopping we get to the house to find my sister in law brought her super sick baby over her kid was having a hard time breathing and is coughing up a storm so my mother in law was like I think he sounds worse than a few hours ago take him to the ER. I’m just standing there in shock at how fucking dumb you have to be to bring your sick kid around my struggling child. I was beyond livid. The ER diagnoses her son with croup which is contagious and thankfully my son didn’t get it.

Now our kids are 4/5 months old and he son ended up spending two nights in the hospital with croup. On Sunday she messaged the group “hey mom we are getting discharged from the hospital now we need to run to Walmart now then we will be over for Sunday dinner what are you making” I was beyond livid like what kind of incompetent parent thinks it’s okay to bring your super sick contagious kid to Walmart then to family dinner and be around my children one of which is still having issues?!?! I seriously can’t be nice I told my husband our baby and I will no longer be attending family functions until flu season has subsided bc his sister is to dumb to keep her kid away when he is sick and I’m to aggressive to not punch her in the face. I’m so frustrated and angry I hate her for many many other reasons but this is sending me over the edge.