Spending addiction is very real but barely recognised yet in this country - which is in no way a defence for the sil theft
You absolutely need to protect mil not saying you don't, but legally you're on dodgy ground taking over her bank account if she has capacity you can't just decide that for her! But sil also needs to be shut out of the account she's treating it like her own money
But sil also needs support to deal with the spending. If at all possible she needs to see a therapist that specialises in addiction.
I'm nc with my sister who has always been bailed out by parents cos she refuses to cut her cloth! Branded groceries, high end and designer clothes for her and dc etc she's either on benefits or in low paid employment (she can't hold down a job)
But I also have a relative who genuinely suffered from a spending addiction which was as a grief response initially. Thankfully they had a good gp and were referred for therapy to an addiction therapist and are now in recovery with "backup plans" if they feel themselves erring that way again - they never stole from anyone though! They racked up some worrying levels of debt and caused themselves a lot of distress.
she didn't seem aware of all that SIL was taking
That's the theft! I'd be livid at that
I think it's financial abuse also
If SIL is helping herself to funds can DH help mum explain this to the bank?
That may cause a lot of trouble - from mil breaching t&c's of agreement with bank to possible fraud dept and police involvement
I've now told him to start learning!
Absolutely! Not fair of him to cast you as "bad cop" when it's his family!
He needs to step up here and stop putting you in the firing line!
His sister has stolen from his mother, he needs to wrap his head around that FACT and stop leaving you to deal with it all.
Does mil know the level of sil income? It sounds like it exceeds hers.
Sil should be perhaps helping HER out!