sooooo pissed!

so I started watching my niece for my brother and his wife at the beginning of February. well here we are the last day of February and my 4 month old was just diagnosed with rsv. last week they brought their daughter over knowing she was sick and just figured it was no big deal. I told them on Tuesday that she had a cough and they just ignored me and now my baby is super sick. I'm so pissed. my husband wants me to tell them I can't watch her anymore but I don't want to start any issues within the family. they only pay me 120 for the entire month any way so it's not like I am making any money watching her. it was to help them out. but helping them out has already cost me an er trip, a doctor's office visit and medications. I just don't know what to do...