Families with Nannies

We have an opportunity to hire a nanny who was previously my son’s preschool teacher for a few months. She had quit the preschool due to management, and we were really sad because although she was his teacher for only a few months, she was an amazing standout teacher who was great at communicating with us and was willing to work with us on anything he was struggling with etc. which was refreshing. She seemed passionate about teaching and our son really enjoyed being in her class. Turns out she’s now looking to nanny, and said she’s nannied for 2 other families before, but no longer has their contact information to provide for references. Is this a red flag? Also, what other information did you request to evaluate prior to hiring your nannies?