You do not have to pay back anything spent on your parent, as long as you have the receipts and it was for her. If you go any buy a couch or something with it, yes, but not otherwise. I have a caregivers contract and learned this from our lawyers, more than one. Best of luck.
...also, I am not sure if you would have to pay that money back if you mother should need Medicaid assistance at sometime in the future. There is currently a 5 year "look back" period even if you have the PoA. All these questions need expert answers if you are going to proceed. good luck
IF you are POA you need to have a lawyer draw up a Caregivers Contract, this will legally allow you to use the money for her benefit and also get paid yourself for her care. Document everything and keep her checkbook perfect for every dime spent with receipt and you will be ok.
There was a while there that my husband and I seriously thought of building onto our house, a mother-in-law apartment for his mom. We had a friend of ours who is a contractor come out and meet with my husbands brother and his wife to talk and see the drawings that he had done. The plan was to sell her house and use some of the money to build onto our house. Brother-in-law #2 was fine with that, but brother-in-law #1 wasn't, even though I was going to be her primary care giver. Oh well. She decided not to go that way, instead she went into asst living. Point is, if it doesn't cause family strife because you're using her money for improving your house (even though it's for her) then the answer is yes, that's what the POA does, spend money to take care of the person who's money it is.
good luck