Debbie is obsessed with your daughter, not Pam. Debbie wants your daughter play a certain role (admirer). When she doesn't play the part, frustration erupts.

Engaging Debbie, even on a negative level, is still attention.

When Debbie says "you act weird", etc. respond with stuff like;

"Yep" or "whatever" or "did you say something? i wasn't listening" or "you go though Pam's phone? that's creeeepy" or " Booooorrrring!!!"

Deflect. Fighting with Debbie only fuels her fragile ego.