My SIL and I have a chequered history but get along very well now. She has a girl a year older than mine (6), they are great pals, play together a lot. She is a good mum, we share a lot of values etc and I know she loves my kids.
While visiting the other day her DD showed mine a scary video. I didn't find out until later that evening when my DD got more upset than i have ever seen her, shaking and crying with terror. She couldn't explain exactly what the video contained but said there was a dead baby. She said her cousin told her she was going to show her a scary video but my DD assumed something with spooky ghosts. She said afterwards cousin said well I warned you. DD was worried she had done something wrong and would get into trouble if she told and said she held it in as long as possible but couldn't any longer as the images wouldn't leave her head. She had to sleep with me with a light on. She's not oversensitive in the normal course of things.
I am pretty angry and it's made worse by the fact that these are relatives and this could get messy. I really want to understand the scale of 'trauma' by seeing the video myself, AIBU to rat her out and demand the name of the video? Also any tips on how to address this with SIL and also DD?