I'm writing as a SD who hates her SM, really hated her for years. From reading your thread the situation was very similar to yours.
Was I messy: yes. Was I disrespectful in the sense that I avoided talking to her as much as possible: yes. Did I have hygiene issues: yes.
The reality is that I was quite a confused kid. My mum was great in many ways but as a career woman with some emotional issues, she probably didn't give me the attention I needed.
I lived my dad but feared my SM whose mood I found so unpredictable. I didn't really understand the rationale behind her numerous 'rules' which my mum AND dad didn't seem to be bothered with. In my mind, she was very upright and particular about things as opposed to my parents who were very much more relaxed about everything.
She was always picking me up in things and I knew she was constantly trying to my dad to 'have stalk with me' except that I knew my dad thought she was upright too, so often didn't rent bothered.
I grew up to feel that she hated me. She didn't but she always appeared cross with me and that was enough for me to want to avoid her as much as possible.
With this I also grew up with very low self-esteem and emotionally confused. My poor hygiene was the direct expression if my own self-loathing. The more she picked up in it, the more I hated myself, the more I let myself go.
What saved us all was me moving to Uni. I rented a room with family who welcome ne with open arms. They focused on the positives and didn't make a big deal of the negatives. I felt loved and cared for and that made me trust their input. Suddenly I went from frumpy to blooming. My hygiene became perfect and I took pride in my room.
In the meantime, my SM faced many issues with her own daughter, 6 years younger. The child who she thought was perfect. No issues with hygiene but with stealing, running away, lying and she realised how much she'd taken for granted how studious, reliable and mature I was.
To cut the story short, we got closer when my dad had an affair. Her daughter blamed her, as did her friends and only I listened to her and told her my dad was in the wrong. Who would have thought!
We are now as close as can be. I don't love her and I still struggle with her moods, but I respect her and can enjoy spending time with her. I can appreciate her qualities. I now know she never hated me, she cared and thought she was helping. She and I are much closer than she is with her daughter.
My hygiene is normal and I take pride in my home. I have faced the frustrations of raising 3 messy kids, one as bad if not worse than your SD! Now much better he's got his own place.
Not judging you or your situation, just giving one story that seems to have quite in common with you.