The last regeneration had been traumatic.
Every regeneration is distressing in some way, but the last one had been especially traumatising. Going from ‘he’ to ‘she’ was a minor detail of the whole ordeal. The last regeneration had awoken a darkness in her - a darkness that she thought she’d long ago buried. After the Time War. After…everything.
The darkness had terrified her. Had almost pushed Clara away. Had lead to returning her Impossible Girl to Earth for her own safety. Had resulted in her travelling alone again.
She’d lost so much - so many.
Yet she knew she’d be unable to stop herself. Knew that when the right person came along she’d once again hold out her hand, offer endless wonder through time and space and she’d do it with only one word.