what causes negative reward points?

Hi, anyone know what causes a customer to have a negative balance for reward points? I can’t figure out how it calculates. Here’s the customers point history:

Earned 256

Earned 2525

Used -2444

Earned 175

Earned -152

I can’t find where it shows a current point balance. Her recent order is the one that says earned -152.

bumping - anyone know?