Reesha was a rosebush-like plant who needed to keep herself pruned to prevent her consciousness from fading and dying. She was invited by the Eighth Doctor to the founding of the Institute of Time.
The Doctor travelled ahead to the end of the universe and found that Reesha and the other members of the Institute had committed suicide. When he returned back to his original time, he refused to tell his friends what he had found. (PROSE: The End)