Dark Page

Lwaxana Troi comes aboard the Enterprise-D as a language tutor for the Cairn, a telepathic species learning to speak aloud, bringing Ambassador Maques and his daughter Hedril, her star pupil. Deanna notices her mother is unusually subdued, and Dr. Crusher warns that the mental strain of contact with the Cairn is exhausting her. Lwaxana keeps relying on telepathy anyway, and after Hedril falls into a pool in the arboretum she collapses into a coma.
Maques links Deanna to her mother's mind, where Lwaxana's defenses throw up false images, including Picard and a menacing wolf. A gap of seven years in Lwaxana's journals points to something hidden, and Deanna pushes past the illusions to find it: Kestra, the older sister she never knew, who drowned as a child while chasing her puppy. Lwaxana relives the loss and recovers, and she promises to tell Deanna all about Kestra. Hilary J. Bader wrote this seventh-season episode, Lwaxana's last TNG appearance.