Stepdaughter got bed bug bites from her mom's house and she didn't tell us!

My SO's ex wife gets her 4 children every weekend. Last week was her first weekend having them, today my stepdaughter told me her "butt was still itchy" and I didn't know what she meant so I took a look and there were bites ALLLL OVER HER! This is 100% bed bug bites! I asked her when this happened and she said "at mom's house... She told me not to scratch them.."

When my SO called his ex she said "yeah I meant to tell you guys, I gotta get that fixed over here" I don't understand. She promised us she could take care of the kids (she's been avoiding them for over a year, it makes the kids sad so we begged her to please spend time with them because it was hurting them) and she pulls this on the first time she has them 😐

Honestly I wish she just TOLD us! I started putting cream on her bites and I'm cleaning down the kid's room.