Would you go no contact with your SIL because she’s constantly getting you sick?

I don’t think it warrants no contact. I would say something and just let her know you’d prefer not to watch your niece again unless it’s an emergency.

My sister and her family are ALWAYS sick. I don’t see them unless they’re well or at a family event. We still call and FaceTime. I will always watch her kids if she needed me (never had to so far).

If you've said something about it before and she keeps doing it, then no contact is an option. With the info you've given, I'd just say tell her you need to know if she or the kids are sick before you come around or babysit

You can catch a cold at the supermarket from a complete stranger, seems a bit extreme for going no contact unless you or someone has underlying health issues.
Just let her know not to come around if anyone is sick.
I feel you though, we've had non stop colds since Feb

when we ask she always says everyone’s fine

whenever we ask if they’ve been sick or are sick she’s said they are all fine.

well she brought her kids over sick when I had a newborn.

Nah I hate being sick. We'd have to meet outside only till she got it together. Some ppl do not have any consideration for others at all. I ended a friendship over something similar cuz she gave no heads up or nothing. Just exposing us and my 6month old

Maybe be more specific when you ask? Like instead of "is anyone sick?" Ask if anyone has had a fever or runny nose in the last week. My son catches colds all the time so when he has a lingering runny nose for an extra week, sometimes I genuinely just don't think about it. Schools allow kids to still come with a cough but not a fever so maybe that's just the rules she has in her head when she says "not sick".

If you feel like she's doing it intentionally or maliciously, that's different of course

I could live without seeing her again. She lives separated from her husband and she is constantly calling my husband over to do basic things. I understand needing help with something’s but she couldn’t even hang her curtains.

If she says everyone is fine and then comes over and you visibly see they're sick tell her nope they all gotta go.

If this is a forreal a constant thing then my answer to her coming over or to her bringing her kids is always just gonna be a no.

Do what you can to boost your immunity and hygiene and the problem may solve itself. Growing up I took echinacea tincture, vitamin c, d, and elderberry syrup and we hardly got sick if those were taken regularly from fall through spring (doesn't have to be exactly that but you start it before the sick season)

Also maybe just ask your SIL to not come over if someone is sick

“I love spreading illnesses” killed me. 😂

But I think your feelings are absolutely valid. My friend’s sister constantly had sick kids and expects my friend to just deal with it. She didn’t go no contact, but they barely see each other now. Her kids gave my friend Covid while she was pregnant. It was awful and her sister didn’t care. She knew that they had it and said nothing until after it was too late. If you’ve voiced the issue and she refuses to be more careful then you need to do what is necessary to protect you and your kids’ health.