Need help writing a letter to mom?

I need to write a letter that will get the point that she is hurting my feeling really badly when she yells at me and tells my to shut up. She makes me feel like I am useless, and that my opinion doesn’t matter. I cry because I believe that she loves my 2nd to youngest sibling more than every one else. I mean, at dinner, he had demanded me, without even a please, to butter his toast, and when I said for him to say please, she began screaming at me. It has gotten to the point that he asks anyone who comes to our house to buy him toys and crap, when everyone knows they are already scraping to get by. And I would like to include the fact that I have a Wattpad account in there as well, seeing as I feel like I am betraying her by not telling. I want her to know that she is making it to the point that I want to literally die, and have considered cutting. This morning I was cooking Ramen on the stove, and since it was right next to the walk way (the stove) i had been a bit out in the walkway while stirring it. She shoved past me and asked why I couldn’t learn to stay out of the f*cking way. So I asked why she couldn’t learn to say excuse me. And then she told me I needed to back off and stop parenting her kids, when I didn’t even do anything! I told her of my suicidal thoughts, and she just brushed it off like it didn’t matter. The previous letters have not worked, and the last one I wrote she chewed me out for, and funadvice is my last resort. Help please? Not only that, I am in high school and the stress doesn’t help my grades, but they expect me to do mine AND my sister’s chores while getting homework done and worrying about my failing grade in Literature, PLUS help with the new baby. Its terrible. On top of that, whenever my mom wants to go somewhere, she drags me with her so I have even less time. Why does she do this?! Its literally killing me!! How do I get the point across?!