I wrote this post out and as I was reading through it all got confusing and it was unclear who I'm talking about at times so I've made some fake names, they obviously aren't the real names. My daughters boyfriend is James, his brother is Mark and his girlfriend is Sophie.
My daughter stays at her boyfriend a lot, could even say she's moved in there tbh haha.
When she first started staying about 15 months ago some of her stuff started to go missing but she just assumed it was just her forgetting where she put things as she was in a different place and it was only small things so wasn't a problem. She stopped staying for 3/4 months due to an illness and only started staying again last week and stuff started to go missing again and this time it was more expensive things e.g a £25 mascara and a £200 pound pair of earrings are a few.
She rang me tonight in tears saying she was driving home because she's found out where all her stuff has been going. She came home and she told me that it is her boyfriends brothers girlfriend. I asked if she was sure and how does she know and she said she is 100% sure, she saw Sophie in James room when she thought they were out and said she was looking for a deodorant for Mark but when James said to him oh here's the deodorant later that day he had no clue what he was on about as he had never asked for it. That was her first sign. Then over the last week Sophie has been "brought by her mum" the same things my daughter has lost. Originally she thought it was just a coincidence when it was just her having the Mascara she lost or the perfume but when she was wearing the earrings yesterday and then anklet today she realised it was Sophie stealing from her. The earrings were brought from a shop that only sells one of everything so you have a unique item and her anklet was made by my other daughter in a jewellery making class at school so I know those 2 items aren't something her mum brought her.
I'm at a complete loss on what to do because I am fuming, some of my hard earned money has gone into those thing she had stolen, but my daughter says she wants to stay home until she calms down a bit then just go over and act as if she doesn't know and make sure she isn't leaving expensive/valuable to her things lying around anymore. She doesn't want any trouble so has asked me to not say anything to Mark and James mum about this as I was about to ring her. She says she obviously doesn't want her earrings back as they have been in someone else's ears, but I spent a lot of money on those and they can be sterilised before she wears them again, and she says nothing else was of value to her or she has repurchased.
I don't want to go against my daughter and speak to them anyway but at the same time I don't feel like I can leave this.