Looks like granddaughter is tired of caring for grandma and does not want all her money going for nursing home care. And, she does not want to pay herself. So, she just resorts to murder claiming she would never want to live that way. I'm sure she would not - especially if she could get grandma's money - what little was left.
And Grandma has a will.
It seems if you don't have a will, they murder you, and if you HAVE a will, they murder you.