You are only human and the situation is so frustrating you are bound to snap once in a while. Just get it off your chest and dont beat yourself up over it.
MIL was obsessed with money. She was used to handling all the finances for her and FIL and always kept a large amount in the house. She has alzheimers and FIL had vas. Dementia. She kept hiding it and forgetting where she had put and we would spend hours searching the house while she accused everyone under the sun of stealing it, so eventually we took it and put it in her bank as she didnt need any because she didnt go out on her own, and although we did not have poa my husband managed all the bills etc for them. Of course she obsessed over it saying she had nothing and no amount of talking or showing her statements could persuade her otherwise. She accused everyone of stealing it and insisted she needed money in her purse so we would draw £50 out for her but it would mysteriously disappear. God knows what she did with it but i remember the shock of the first time she accused me! We had just put £50 in £10 notes into her purse and showed her. 5 minutes later she got it out and looked at it and asked where the rest had gone No no amount of talking or counting would convince her otherwise. She turned to me and said we both known youve taken it !. I know she was ill but that cut me to the bone. So the end we solved the problem by printing out a wad of £20 notes on the computer as she didnt known the difference and if they vanished we just printed more!
Its a horrible disease and a horrible life for those living it and everyone connected to them. Even a saint would lose their patience and i dont know why we expect to be superhuman and not get frustrated or cross from time to time.