What would you do?

I'd let her fetch her undisciplined defiant child. She was always going to cry and get her mother to come because clearly her mother has yielded to her tantrums. That's why she is so defiant. She's used to getting her way. Her caregivers have enabled her negative behavior as opposed to shaming it. She doesn't recognize adults as authority figures,she sees them as people she can manipulate with her behavior in order to get her way. The older she grows the bolder her lies and manipulation will be. For your own safety don't host her again unless you have cameras in the house to disprove any claims she may make. She's already displaying vindictive and abusive behavior,she's not to be trusted. She needs some sort of therapy.

She is probably on her phone all night long. If she cannot respect your household, then it is just as well that she go back home. Sorry it couldn't have been a better time for you all.

A squirt bottle works well to get a kid like her up. That mum is in for a battle if she’s already like this. I care for teens like this, it’s challenging to say the least.