I am all for actions having consequences, like seriously there needs to be consequences. But you NEVER punish a kid/teen by grounding them from family time especially during the holidays. That's not punishment. That's alienation. And alienation is abuse (if they're your kid and a minor).
Your first mistake may have been that you didn't consult her father concerning what should be the consequence. Now if he's the kind of parent you can't co-parent with. A simple heads up of what she did, and that there will be consequences. It might have stopped him from buying the iPad (maybe, again depending on him being one of those parents).
I would hold her tablet ransom instead. She doesn't get to use her iPad until she's replaced her brother's or, give her the alternative. She can give him her iPad and you'll give her the half you were going to contribute towards an iPad for her. Let that be her choice and if you could, kindly inform your ex that he needs to have your back here. (If you can)
But yeah...YTJ over the punishment and your ex and daughter suck too. She sucks because she manipulated the situation and destroyed her stepbrother's iPad, your ex sucks for what? Buying her an iPad after what she pulled, and not being willing to contribute toward his child. It's 50% his responsibility just as it was 50% yours and that means it should be 100% on your daughter. Because that is so wrong!
My best friend lost his wife over a year ago. He started looking around for company and companionship about 6 months after she passed. A lot of people thought it was too soon. I even thought it, but kept it to myself. I've never lost a life partner. I couldn't even begin to understand what a loss like that is like. I do know my friend though. And he was one to never be alone. Not that he wasn't alone at times, but he wanted to be an a relationship. He didn't want to be lonely. Some people just don't like being alone. It doesn't mean that you're SIL didn't love your brother. But she's lonely and he's gone and not coming back. I imagine she went through all the stages, maybe even feeling guilty for moving on. You all get NO say in how she lives her life. And just because you feel how you feel, doesn't make her evil for trying to live life and move on. Would you rather her be a mess for the rest of her life to prove her love for your brother? Wth? YTJ.
NTJ. Tell your brother to mind his own business. Precious snowflake doesn't get to have ex BIL at their boys weekend, poor baby. It was your ex's time with his son, it doesn't matter that he was taking you all on holiday. If he was doing what he should his answer to your brother would have been "sorry bruh, It's my weekend with my son"
Your brother and ex are buttheads