WHO FED HERMIONE WHEN SHE WAS IMPRISONED AT HOGWARTS?
Umbridge via the house elves. She was lying when she told Healer Stroud that she'd forgotten Hermione. She had Hermione fed like all the other prisoners, thinking initially that Hermione would be forgotten after a short time and she would be free to do as she pleased with her.
Instead, Draco, Snape, and Montague kept trying to track Hermione down and submitting official requests for her prison records, forcing Umbridge to keep denying that Hermione was at Hogwarts in order to cover up that she'd tried to steal one of Voldemort's prisoners.
When Voldemort specifically demanded that Hermione be included in the Repopulation Program, Umbridge had to either admit she'd lost a prisoner, or produce Hermione with an excuse about forgetting her during the post-war upheaval. She chose the latter but her lie was obvious since Hermione had been kept fed the entire time, which was why Stroud and Voldemort never believed it.