AIBU or is SIL!?

[Emmy5159]

Long story short...
DD has been unwell for a period of time in and out of hospital picking up every thing constantly on antibiotics.
Found the problem FINALLY!! But this week she has been poorly again and turns out she has hand foot and mouth.
DS had it last year and gave it to DN. SIL has had a new baby 3 months old, baby was poorly and had a stint in hospital last week with bronchiolitis baby is all good now thankfully!
SIL was annoyed today that grandparents were coming around to see DC as they won't be seeing them on Christmas as I don't want SIL DC to become unwell.
SIL said that the baby will still catch HFMD because the adults will be with my DD.
Was really pissy. Which pissed me off.
AIBU?

I think you all have earned the right to be really pissy. You with all your children's health issues, and your SIL with a sick 3 month old. You really can't understand why she would be distraught at the thought of her baby getting sick again?

Who was SIL pissy with? She's right in that PIL can catch HFMD from your dd who could then pass to the new baby, but she shouldn't have been pissy at you. Unless you asked PIL to visit?

Some adults do catch HFM and it is very contagious. If your SIL has had a very poorly newborn, then I think it’s understandable she is so cautious. I also think it’s very understandable that you are staying away because your DD is contagious. Neither of you are BU.

She shouldn't have been pissy with you, but I can see her point. Yes, your parents could carry it. It would make more sense for them to visit you on Boxing Day, after they've been with the baby, rather than before.

I think you SiL is in the right here. My DH caught it from our son - adults definitely can get it and therefore pass it on. I guess maybe she could have been nicer about it, although I'm not clear from your OP who she got 'pissy' with?

She was taking it out on me.
I definitely did not ask PIL to visit I said we would stay to ourselves until DD was better.
I completely understand she doesn't want baby to be poorly again although she has taken her out all winter with no hat and decided to go out to winter wonderland this evening with baby only recently being out of hospital.
So swings and roundabouts I guess?