Chloe, I just want to give you a big and say don't be hard on yourself for thinking and feeling the way you do. I found the two years between 18 months and 3.5yrs to be the hardest toughest parenting slog ever and I'm sure I had plenty of uncharitable thoughts about my DD during that time.

One thing that helped when my DH was away overseas for several months and DD was acting out: I contacted the local behaviour support unit. A lovely worker came out and observed our dynamics and gave me some strategies that turned DD's poor behaviour into consequences that affected her and they worked really quickly. Her behaviour was not even that bad, just that I was unsupported and not feeling like I was coping. The worker was lovely and gave me lots of positive feedback for where I was doing the right thing and really helped to have someone to debrief to. Might be worth a try...?