Do I tell my sister my mom doesn’t want to see me at Christmas?

My mom’s going through chemo. I was visiting in November to help take care of her, I live a few hours away with my husband. She was pretty much “I’m not seeing anyone at Christmas” because any sickness could land her in the hospital and delay her end date of chemo. She’s in remission which is great. We knew my sister(has a newborn) would be upset with this but I was ok with it because we both couldn’t see her.

Both our MILs host Christmas eve so we see my mom Christmas Day. We do spend the week of Christmas at my MILs because everyone has it off(siblings, mom, nephew ect.). My mom called me 2 weeks ago and said my sister was coming for Christmas Day and when I got upset she told me that I’m more exposed at my MILs house and that my sister is going to her MILs house but should anyone have a sniffle she’s making her husband and her skip. She also said everyone there is everyone who was at Thanksgiving. I felt like I was pushing her into something she’s not comfortable with so while she finally was like “you can come” I don’t think we will go. I asked her to ask her doctor on her appointment on Wednesday.

So yesterday at our family Christmas party(mom’s side) my sister asked if she’d see us Christmas Day at our moms. I told her I wasn’t sure because it might be too many people and she got defensive and I said she had to ask her doctor so she goes “well we’ll see you at some point over the break”I didn’t want to get into it at the party so I figured I’d let her know over text that I don’t think she wants to see me or my husband because his nephew is in school and she thinks we’re too exposed being there. I’m bummed that she suddenly feels my sister is ok to see her(my sister just went away this weekend) and we’re not but trying to be ok with it.