Would you expose 1year old to chickenpox?

So a little bit of backstory here, I'm currently 17weeks pregnant, my partner and I have a 14month old son.

Partner has a 3 year old from a previous relationship who stays with us every weekend and longer during school holidays. Relationship with her mother is strained, just finished court to get a court order to prevent her denying access. Also waiting for a tribunal about maintenance payments (partner has always paid his way for his daughter)

So last week partner and his ex had a little text argument as we received a letter about the tribunal and he wasn't pleased she was going ahead with it. Then suddenly daughter has a sickness bug and can't see us that weekend.

Now this weekend we are meant to have her longer because of school holidays (out first time having her for school holidays since court order) and now her mother says she has chickenpox.

Her mother says we shouldn't have her as its a risk to myself while pregnant and to our son.

I'm not very concerned about the risk to myself as I know I've had chickenpox before. I am slightly concerned about the risk to my son, he is still young.

But hear me out, if she lived with us permanently, we would have no choice! There would be no option to not see her and not expose our son. I just feel guilt for not seeing her while she's sick because if she lived with us of course she'd stay with us and we'd take care of her.

Partner doesn't know what to do as he's damned either way.

Also to me seems likes partly just excuses to deny access as she's not happy with him about maintenance and about us having another baby.

Any advice?