As long as she didn't have any health issues that might interfere w/her nanny duties OP, by all means, I would give her a chance.
In my opinion as a mother, I much prefer to hire a nanny who is older and has actual hands-on, real life experience successfully raising her own children.
I know there are some 20-somethings that make good "big sister" type babysitters for school-aged children and that is fine w/me. But for infants and toddlers, I would much rather go w/someone who has already raised children. I prefer someone who actually has
experienced each stage of a child's development vs. learning about it in a classroom. This person would be less likely to call me during the day to ask, "Help!! What
do I do??"
I cannot think of any cons. The only one is that as we get older, we tend to have more health issues, but I don't view 51 as too old to be a nanny since w/all of our modern medicine these days, people, esp. women, are living longer and vital lives.
So go for it.
Hire her.