I want to start by saying that I am a 15 year old girl, the oldest of 3 full blood related siblings, and my parents got a divorce three years ago. Both of my parents remarried and I love my step dad, but I can't stand my step mom. It makes my dad upset that we don't get along but I don't know what to do because I honestly hate her. Let me start by explaining my relationship with my dad.
When my parents got a divorce my dad was a wreck. He became an alcoholic and depended on me for support. He would constantly talk (and cry) to me about what he was feeling and I had to hold it together for the whole family. Although that was really hard for me to deal with, being about 13, my dad and I formed a special relationship and I love him so much! I am definitely a daddy's girl! Long story short he tried to move on with a couple serious relationships that didn't work out and I was left, again, to pick up the pieces for him. He had told me many times that if there was ever a girl that I didn't like that he was dating, I could tell him and he would stop seeing her. That, however, apparently didn't apply to the one girl I didn't want him to see! Her name was Crystal. She was 26, an on and off stripper that had two small kids with two different dads that she didn't have a serious relationship with. Well her and my dad ended up getting married 5 months later. 
Alright, the reason I don't like her is not because she is/was a stripper, I don't like her because she is lazy, untrusting, and immature (among many many other things). Some of those things may seem small but they really aren't when you have to live with her constantly! Let's start with being lazy. Remember how I said I had to hold things together for my brothers and dad? I was practically their mom when we went to his house.  Well nothing really has changed with the marriage except that now if I forget to do something like the dishes I get in trouble. My dad says that it is because "Crystal likes the house to be clean" (even though she obviously doesn't care enough to do it herself)! She will literally just sit on the couch eating chocolate while she watches everybody around her clean! She is also very untrusting. She always thinks my dad is cheating on her! For example, whenever she finds something of mine that she doesn't recognize, she immediately assumes he is has a girlfriend! The other day she found my bathing suit top in his truck and freaked out, screaming and cussing and I had to tell her it was mine! Another thing that she does that drives me crazy is that she is simply annoying and immature. She seriously acts like she is twelve. She is always playing stupid trying to be cute, or fake giggling, or squealing like she is six. She doesn't realize that when you are 27 it's not cute anymore! Honestly, if it were just that she annoyed me, then that would be fine and I could just suck it up, but that's not the case.
The thing that makes me hate her instead of just dislike her is that she is plainly cruel and mean to my dad. My dad is already insecure about being smart (he has ADD and usually forgets to do things). She is always cutting him down in little ways that he doesn't notice, but I do. For example, she purposely makes him look stupid in public and she always blames him when there is a problem (even if it is as simple as losing her keys when they are actually on her dresser where SHE put them). I didn't hate her though, until Friday. (important background info: when my dad was trying to move on from the heartbreak of my mom he dated a couple of his ex students whom he hadn't had contact with since they graduated) When Crystal found out about this, for whatever reason, she freaked out. This wasn't just a little argument, it went on for three days. the first day started at about midnight and I had no idea until the next morning when my dad was working. (The very mature Crystal *cough* left her 7 year old in charge of her sick 3 year old while she went to the gym to tan) I was asleep in my room when they woke me up to make them breakfast. About halfway through pouring their cereal Crystal got home. She walks into the house on the phone, screaming at my dad. The first thing I hear is "OH SO JUST BECAUSE THEY WERE YOUR EX STUDENTS THAT MEANS YOU CAN F**K THEM!?" I was shocked! Then she goes to her room and I (along with my 10 year old bio brother, 7 year old step sister, and 3 year old step brother) can hear her screaming "YOU WANT TO KNOW HOW I FEEL!? I FEEL LIKE YOU JUST RIPPED OUT MY HEART AND STOMPED ON IT!" At this point I was annoyed but not extremely pissed-- yet. The next thing she tells is "I ALSO FEEL LIKE YOU ARE SICK, DISGUSTING,  PERVERTED, NASTY, AND I DONT FEEL SAFE AROUND YOU!!" When I heard her say that I didn't know what to do I was so mad! I felt like I was having a panic attack. I couldn't stop shaking and I was having a hard time breathing and I yelled "YOUR HAD BETTER NOT BE TALKING TO MY DAD!" I was so upset and I ran to my room and shut the door. When I couldn't calm myself down I went outside in the front yard and called my boyfriend, who made me feel a little bit better. I knew my mom would be picking me up in fifteen minutes, so I packed the clothes I wanted to take, got my brother, and waited outside. I have been at my moms since, but I have to go back tomorrow. I am still so upset and dreading having to be in the same house as Crystal. 
Anyways, the reason I am posting on this site meant for step parents (not step kids) is because I want to hear what yall think about this. I am not trying to slam anybody or step on toes, I just need a different perspective on this situation; I thought hearing from people in Crystal's position could provide me with this! Thank you for your time!