D.M.
I looked up info on shingles on the internet at mayoclinic.com. Shingles is contagious and could cause chicken pox in your kids...even if vaccinated. If grandma has a bad case, she is unlikely to want to visit, although, she may have recovered adequately for that visit.
I would look up info on the chicken pox vaccine at www.nvic.org. This vaccine really is totally unnecessary. CP is a very mild disease when contracted as a child, but can be deadly as a young adult. The manufacturer has suggested that boosters will be necessary as they do not provide adequate or long-lasting coverage as a child ages. It still does not convey 100% immunity in any case. The best vaccine in the world is our own body making antibodies after we contract cp.
So you'll have to decide how much risk you are willing to take. Grandma is no longer contageous if there are no open sores. Good luck and I hope Grandma can see the kids.
Feel free to contact me if you have any other questions. I work with many docs and health care professionals in the area of prevention. I'd be happy to help. In health, D.