Is her criminal record clean? Driving Infractions? What about previous employers? Does she have legal working status? Should you have an attorney approved contract/work agreement?
As well as a complete background check is imperative before your child is left unsupervised with a caregiver! Just because a "friend" referred her or a couple of moms on social media said she did a good job doesn't mean that information is enough to leave your child alone with her.
Can't always tell you when something is wrong. Do your homework before you hire someone to assure the best Nanny for your family & the safety of your precious little ones!