my daughters found their step sister after their dad walked out on them many years ago. they wanted to meet up- i told them she could come here to see them.
i found out later her mom flew off the handle, had a real fit, etc. she said to me- i can't believe you would have me in your home. i told her it was for them, not me.
found out the dad (dirtbag) had actually adopted her- I am still mad at him for walking out of their lives but even more so for adopting her when he had 2 daughters.
when my daughters got married, she came, she calls me mom and says i am nicer than her mom. i tell her she's one of my "extra" kids- my extended family and always welcome here.
the kid's dad is #1 on my "when murder becomes legal" list. even more so now. :)
moral of the story- go for it grannie! you may just end up with some more love to share you didn't know you had.