Weirdest trainer advice so far. Who knows what they put her through. The fact that she is wild for so long after she sees you is a red flag to me. When I pick up my dogs from the breeder's boarding kennel, they are happy to see me but in the normal range of "happy".
It reminds me of a situation in the past when I picked up my dog from boarding at a vet's office and he acted like that. Then I found out that he had been crated all that time instead of all the good and social play they promised.
I would never leave my dog at someone elses unless he had to be boarded when I go places where I can't take him.
It sounds like your trainer has too much power over you if you cannot standup against her/him. Trust your gut and stick with that.
Deja, GSD, sable WL, female, born 11 / 2013
Cam, Rough Collie, sable, male, born 8/2015