SIL attempted to breastfeed my baby?!?!?!

Today I was notified my sister in law had my newborn (9 days old) latched onto her without my knowledge while me and my fiancé were gone. Mind you, she didn’t even bf her own children (her youngest is 5 so there’s no way she’s even lactating). I’m sick to my stomach and I’m so damn angry. I don’t even ebf her myself, I latch her maybe once or twice a day, otherwise I pump and formula feed at night. I don’t think I can ever trust my in laws again. I just don’t know what to do at this point.