Ending a friendship

I've never been good in the tact department. Some people just seem to manage things so gracefully and II could really do with some helpful suggestions here.
I have a long friendship (we were at school together 50 years ago!) and have stayed friends even though I moved away. We used to meet up 4 or 5 times a year when I went back to visit my parents and wrote, then text mostly or a phone call.
Then 5 years ago my friend became a Granny and has been very involved with supporting her daughter. We have only met up a couple of times in those 5 years - we arranged more but often she had to cancel because of family stuff and texting has been sporadic.
Now both grandchildren are at school and she suggested a meet-up and frankly it was awful. We just didn't have anything in common. Her conversation was mostly grandchildren. I've had a fairly life changing few years, widowed, gave up work, been travelling, moved house - nothing that she could relate to either.
Now she's suggested we meet regularly as we've both got more time. I don't want this friendship to end nastily but I don't really want it to continue. At the moment I haven't answered that text but ignoring her isn't very nice is it? Or is that better than making excuses or just saying the truth? Help!