This is Samuel and I will discuss this and provide you information in this regard.
I am sorry to hear about your wife's health.
I suggest that you will first need to file for a Guardianship
over her. And once you are appointed her Guardian, then you are able to sign her name in front of a Notary who will have her acknowledge that she understands the document and what the results will be.
To get the Guardianship you need to go through the courts. You can ask the clerk of the circuit/superior court in the county where you live for the documents to file pro se
and they many have those forms. However, it can become complicated and you may want to consider at least consulting with a local attorney to assist you.
If you wife is able to comprehend and her mental ability is not damaged by the stroke then you should be appointed her Guardian.
Please note that I can only provide information for what you ask. In that regard, if you have other questions or need clarification, please post them here. Otherwise, I appreciate your Positive Rating as that is how I get credit for my time and information.