WMG / Avenging Spirit

The Girlfriend's abilities didn't emerge until the boyfriend was there to give her encouragement

It is possible that the Girlfriend suffers from self-confidence, and it was because of this that she wasn't able to use her weapon. She could have always freed herself, but without her weapon, she knew she would have been immediately incapacitated, or worse. It was thanks to her boyfriend that she was able to unlock it. Even after he leaves, she felt confident to be able to use it again, and to further improve herself.