Caring for a loved one can be challenging and feel confronting - she is your wife, and I presume for the past 20 years you have shared and discussed many things.
I wonder if her medications may be affecting her behaviour or whether this is just an expression of frustration from no longer being able to perform tasks around the house - and some people are known for being 'particular' in certain regards (think about some of your own quirks and then imagine another person trying to replicate them).
Your subjectivity and intimate understanding of each other can leave you rather exposed to manipulation (and wary of conflict) and you do seem to be burning the candle at both ends with her needs (in the form of criticisms) affecting your motivation.
Could her condition warrant a more objective or specialised carer - perhaps only for a few days a week to give you a break to recharge and provide the best care you can without the stress.
Your effectiveness as a carer begins with managing your well-being.
While I was caring for my father in his final years, I had prepared to 'transition' my role progressively to more capable carers in line with his decline and ever increasing needs. By the end, I had quite a team of people providing many services beyond my capacity (and skill set) for which I was very thankful as they made his life more comfortable while I could continue to provide familiarity and emotional support.
