I can't help but wonder why you are even second guessing yourself with this? I do understand that sometimes we forget what evil looks like when we are so far removed from being that way. All I can say is man when you get to feeling like maybe she deserves to see the kids think back to the worse day they were in her care.......
As some have mentioned asking the kids what they would like, please don't! Kids all want a mommy and long for that and maybe even remember her at her best, but it would be a cruel thing to give them hope because she lost her mommy card the first time she ever abused them. Remember that.
Now go have a nice holiday and quit answering the phone when she calls, you owe her nothing! You do have the responsibility and privelege to make a nice life to your children.