Romana was thinking about Gallifrey, and this angered her.

Gallifrey was the home planet of the Time Lords, the home of Romana and once - although she sometimes found it difficult to believe - the home of the Doctor himself. That belief wasn't easy because the Doctor seemed to be the very soul of nonconformity, while the Time Lords as a race were...well, very worthy, but dull.

The reason for her anger? Gallifrey kept pushing its way back into her thoughts, claiming her attention while she tried to concentrate on the problem of the void. No matter what deductive method she tried to apply to her problem, everything failed for lack of information and then Gallifrey, the world that she'd been hoping never to see again, would rise in her thoughts, unbidden.