Do some harsh punishments inflicted upon the cat, followed by remorse and seeking forgiveness, affect the reward of its caretaker for looking after it? And will Allah forgive her for that? And is she sinful for her brother harming the cat despite her attempts to prevent him?

A person is rewarded for being kind to animals and punished for harming them unjustly, as the Prophet, peace and blessings be upon him, said: "In every wet liver there is a reward," and his saying about the woman who was punished because of a cat: "Neither did she feed it nor give it drink when she imprisoned it, nor did she leave it to eat from the vermin of the earth." You must fear Allah concerning the cat, and if you are unable to protect it, leave it free to save itself. Sincere repentance determines forgiveness or punishment.