need advice

so my husband told me this weekend we are going to his mom's this coming weekend I told him that's fine we can, we are suppose to meet his mom's boyfriends daughter but I seen on her Facebook that she is sick with a bad cold she is pregnant so she can't really take much for it. my daughter is 3 weeks and 2 days old.. And I told.my husband yesterday we aren't going to be able to go cause his daughter is sick and I really don't want my daughter getting sick, and he said that's fine he understands and he'll let his.mom know last night well his mom messaged him saying shed be here early.to pick us up! so I'm like oh maybe his daughters not coming cause she's sick so I messaged and asked her and she's like yeah I'm going to my dad's and I said we got invited but we can't go.. I'm pretty upset and feel they are trying to go behind my back and show up this weekend and be like well they come to get us so we have to go... And I'm not okay with that.. I'm trying to look out for my daughter's health!!! how should I go about this ??