Aw, Lisa, you've had a lot on your plate - roller-coaster-y. My mother-in-law passed away in 2022, and she had an unbelievable green thumb. We gave her a small white rose bush years ago, which she nurtured into a large, beautiful shrub. I planted a white rose in my yard in her honor; let's hope I can keep it alive and nurture it as well.
Did your daughter's mother-in-law have a favorite plant? If nothing specific, I would recommend a perennial, something that either blooms or otherwise brings color. Where she passed away recently, you could plant a red twig dogwood, that would provide color in winter. Or perhaps an area of your yard with varied daffodils, bringing spring. And roses are always nice, if you have any luck with them.
You are stretched a lot of ways now, but in a few years, you'll be taking that granddaughter out in your yard with a kid sized trowel, and showing her how it's done.
☮️