I too would recommend caution before making accusations.
When my OH took over his mum's finances last year, he discovered she'd been handing over substantial sums to his younger sister each month for some time. However, his mum knew what she was doing, she knew her daughter really needed the money and it was her way of thanking her for her day to day care.
OH was a bit put out at first (and elder sister was pretty upset) but only because it came down to the old grievance of all three siblings not being treated the same. But the point is, my MIL knew exactly what she was doing and, at that stage, it was her right to spend her money as she wished.
Since OH had LPA, this has now stopped as there was clearly no justification for the gifts since MIL moved into the CH.
So I agree with the others. The best way to sort this out is by getting a LPA or deputyship asap and all transactions should then become more transparent.