@ilovewings I say this with affection, and I regard you as someone who is as cautious as I am when it comes to Covid.
I, too, want to live in a fortress of solitude ((TM Superman) and keep myself and my loved ones safe from harm.
Again, I do not want to know or delve into your business. I say this as someone who is not a stepmother, but my husband married 7 years after our divorce and I've had to deal with my daughter's stepmother (decades ago). No pandemic back then, so it's very different, but I do have experience with the push and pull of stepparent involvement.
I admire how protective you are of your husband. But IMO as
@justbeachy noted, your husband is the pivotal person in this. I presume he loves his son and daughter, who were his family before you (again I mean this delicately) and he may resent you prohibiting your stepdaughter from seeing him.
As
@LaborDayRN noted, I think a PCR test before she arrives would at least alleviate your fears of whether she's contracted Covid from working in a school and having teenagers. I took a PCR before I visited my parents. It's true that you won't know if she catches anything on the plane or in the airports, but it would at least reveal if she has it prior to arrival.
As
@Teche noted, your husband can at least keep YOU safe if he stays elsewhere during their visit, follows all mask rules, and quarantines at home. Of course you're in anguish about his safety and you resent his daughter for putting you in this quandary, after all you've done to stay healthy.
It's clear you're in torment about this. I don't blame you. But IMO your husband probably wants to see her and you don't need to jeopardize your happy home. We were happier in the AirB&B than the hotel, because no strangers were coming and going. That would be my choice in this situation. Let him see his daughter before your remaining years with him are filled with strife. Have him stay away from home during their visit and quarantine at home afterwards. Make him get a PCR test when the quarantine is over.
I know you don't care about any of this because you don't want him to be with her, period, due to wanting to keep him safe. Understandable. But she wants to see her dad. I understand that, too. She lives in a different state, and she is also worried that something could happen to him and she wouldn't have seen him. You're afraid she will be the cause of something happening.
IMO it's very clear that your husband is the central person here. Exempt yourself from his decision and keep yourself safe.
I'll shut up now.