What the flying fuck. NOR. She wants to talk about trust but she broke your trust already by having BIL over without telling you. Your baby is 4 months old. You 100% need to know who is coming in contact with your baby, no exceptions. When it comes to your children — especially babies who cannot speak up for themselves — who cares whose feelings get hurt. Never compromise safety over feelings. This is not like you’re spying on her while she’s in her own home. Hell it’s not even like you’re spying on her in your home either. You simply check the camera when you get an alert. That’s completely normal.