It is possible and from what I understand the longer its been since you had it done the more your chances of pregnancy increase. The chances are still small, but there none the less. You need to take a test or have your doc do blood work to know for sure.
Congratulations on becoming a grandmother!! As for pregnancy after tubal ligation, yes it is possible, just not very common. It is however, important to find out for certain as if you are in fact pregnant, you are at a much higher risk for a tubal pregnancy and that needs to ruled out. The best thing to do would be to either take a home pregnancy test, or have your Dr. run a blood test to find out for certain. Good luck, I hope you get the answer you are looking for.