Covid Co-Parenting

Wondering what others would do in this situation. My stepdaughter just showed symptoms of Covid today (Tuesday) and tested positive. She hasn’t been in our home since Saturday she’s been with her mother. Her 5 year old sister went back with them yesterday not knowing that her sister was positive. Her mother believes we should take the 5 year old here so she doesn’t get sick (remember they were together yesterday and this morning so she’s already been exposed). I say no way because I have a 5 month old who is obviously not vaccinated. The Mom is now calling my husband a bad father for leaving her there to get sick. Just wondering what you would do in this situation?