As I read this, if you have no mortgage either way your income stream will support you, barring anything unusual.If she dies I lose about 20% of my income stream. If there is no mortgage then my income stream will sustain the property until I can no longer do the maintenance, at which time I will have to sell it and move into an old folks home.
If I die first, and there is no mortgage, her income stream will support the property. She would not be able to sustain mortgage payments. Nor would she be able to care for the type of property we are looking at.
The alternative if you took a mortgage would be you then have cash which to invest and pay off the mortgage. There is obviously some risk to this.
You could invest the cash in various fixed income or cash instruments at rates that currently lag your mortgage rate. Obviously that isn’t optimal. Also your investments may be taxable and mortgage interest likely not deductible.
You could do the mortgage and hope that in time rates go lower, sooner or later they probably will, and refinance to a lower rate. Or rates could go up and your mortgage is locked in but cash and short term bond rates increase.
You could do the mortgage and invest some of the money in stocks. Obviously that could work out but is even more risky.
It doesn’t seem there is a ton of upside to mortgage in your situation. If you did maybe I’d do half. My answer would probably be different if rates were very low like they used to be.