Intense germophobe mom wants to bring baby to rehearsal dinner

This mom is a great friend who had a baby a few months ago. She's always going on and on about how nobody is allowed to touch her baby, not family, not friends, no touching of socks, no standing too close, and not breathing too close. It's...a lot. She has every right to do so, but its gotten so intense that I want nothing to do with her son, because all I would think of was the liability. It's sad but of all my friends kids that I love so much, I feel nothing towards him due to lack of bonding. This is the same mom that hugs and shakes hands with everyone and then touches her baby without purell or washing hands (eye roll).
Anyway...for such a germophobe who doesnt want anyone to as much as look at her kid the wrong way, she wants to bring him to my rehearsal dinner! Like, what? She has child care here and is using it for the wedding. I almost feel like she wants to sit there at my RD with an adorable baby that everyone wants to see or hold or what-have-you, and reprimand everyone (my loved onee) who doesn't abide by whatever rules she's set.
Anyway, we may be having another baby there, but I dont want the liability of her baby there because if he gets sick then we know who she will blame, and I dont want to think about that crap the night before my wedding. How do I tell her that she cant bring her baby?? Is saying "I'd be too worried about exposing him to germs" too passive aggressive? What would you say? I guess this is part gripe, part wwyd!