1.5 year old will lose her favorite person

This is a request for advice about grief.

My mother is dying. Realistic odds seem to be a month or two. She is, beyond a doubt, my 20 month old daughter’s favorite person in the whole world. My mom has at minimum seen my daughter every other week (or so) for my daughter’s entire life. When we go to my mothers’ house she searches for my mom.

How do I help her to understand, after, that grandma isn’t here anymore and won’t be here again? How do I do it without it tearing me apart from the inside?