I'm thinking of refusing to sign a form saying a trainee completed her hours, because she refused to follow my instructions
But didn't she get the training done right?
She completed the hours but I do not like her.
If policy says she should pass you need to let her pass. It is not good to disregard company policy.
Screw the policy, I'm going to ridicule her by sending her back to her trainer.
You need to let her pass since she did the required work. If you hold her back you have to spend even more time with her and you said you didn't like her to begin with. Discrimination is a fineable offense.