They need the bodies that badly. I don't know the exact science behind it, but I think we'd all agree at some point you have to weigh between bringing no one in, and bringing in some sick but fully vaccinated people.

Thankfully it sounds like OP's sister is vaccinated so she should be fine.

My takeaway from this: it doesn't hurt to call someone out at your office if they seem sick. "Hey, you sound kind like you might be sick. Did you consider asking for a day off?" They might not have even realized it. You could probably also raise the issue with a manager.