you have a choice of trying to get to the bottom of things, which is likely to need a lawyer plus accountant and get expensive very quickly, or cut her from your life and move on. If you're genuinely happy with the money side, choose the latter. Life's too short and getting the full story isn't going to bring your parents back or undo any shenanigans she may have been up to while she had POA.
GD answer: build a big patio.
With a corner set aside for queen wasps and a free-standing door for the absolutely necessary letterbox.