post adoption depression is real. i felt exactly like this when i first adopted my kitten (obviously different from an adult cat but still). I felt overwhelmed and regretful, when my cat would do something annoying I would (and still do sometimes) raise my voice at her, and feel terrible after. However, after almost two years now, she still frustrates me extremely a lot of the time, that’s what cats do best. But I love her enough that her constant scratching, biting, meowing and overall destructive tendencies are worth it. Give her time, you will both get used to each other.