Yup it's happened to us all.
Don't let the kid see one iota of concern on your part. If you add ANY energy to this it will get worse.
Do you have the ability to video her on your phone? If you do... tape her for a minute right after her mom leaves and send it to the moms phone immediately. Give her a video of the kid being perfectly fine as soon as she is gone.
That solves it with the Mom.
If the kid continues then do the Buh Bye Outside Program on her:
https://www.daycare.com/nannyde/the-...in-daycare.htm