Yes, she thinks she has a buddy back in her cage, so might be reluctant to leave her friend.
Many birds have mirrors in their cages. There's nothing wrong with that. But during training, they usually make sure that there isn't one in there. They recommend waiting until after training is complete, and the bird already has formed trust in you, and a good bond. Sometimes you have to take it back out, if she starts showing a preference again for her "buddy", rather than you.
Good luck, Eleni