I have a 10yr old stepdaughter from my husband previous relationship and I have a 13yr old daughter from previous. Me and husband now have a 3 yr old daughter. Recently I was tidying up the older girls room and when I was putting socks into my SD drawer I saw a book might be her diary open and in highlighted capital letters said FU to her little sister and her dad also stating how much she f*cking hates then. So I was concerned and read the rest it stated that she wants to kill them and that she hurt my daughter by throwing a box at her lip bruising it but lied to her dad about and that she did not care that it hurt her. My SD is very quiet, shy, very isolated to herself I always have to ask her if she’s ok I always thought that there is something going on with her, a gut feeling something is wrong but I just always ignored it and thought just the way she is maybe which makes this situation very scary to me. We are going to get her help but I am now so angry because my 13 yr old warned me and I ignored it and it’s about her stepsister always picking at the little one and sometimes hurting her for no reason. It’s like all the other times when my SD and her little sister are alone and her little sister ends up crying all the time and we always wondered why and now it all adds up. My 13yr old has also expressed to me that she doesn’t want to be around my SD lately cause of her weird behavior but I didn’t believe her. Cause my SD played the part so good of being a sweetheart and being such a good girl. I am scared and angry that she has been doing this playing the part. Her dad gives her so much love and attention my husband is obsessed with his kids and loves them so much and including me and her sisters too we treat her with love so I don’t know why or where this behavior is coming from. We are going to talk to her when she comes back from her mom and made an appointment to see if she needs therapy but I just feel sick to my stomach and I don’t want her near my kids. I feel like I got played I don’t know what to do?
You were played by a 10yo. Your anger is justified, and your fears are realistic. This is not a situation that anyone wants in their family, and it is tough, but you are not to blame, you didn't cause this.
You didn't want to believe that your SD was doing anything wrong, and, yes, your inaction caused this situation to go on longer, but that's water under the bridge, and you're awake to the issue now, and now you and your husband can help all of your children recover.
Your 10yo SD is angry and taking it out on your 3yo. This is not ok, never ok, but it is something that a hurt and angry 10yo child will do.
Your SD has gotten away with completely unacceptable behavior, and she needs to know that you now know the truth about her hurting your 3yo, and she needs to know that it will stop either because she stops or you will make changes that will stop her from hurting her sister or anyone else in the family.
At the same time your 10yo is herself an hurt child. This is what her behavior is telling you. While it's hard to overcome your very justified anger, your 10yo SD desperatly needs you and your support.
Support does not mean your tell her is OK, because it's not. What you tell her is that it's not OK, and you will not allow this situation to continue.
You have every right to tell the 10yo the truth of how you feel. You have a right to tell her how sick it makes you feel, and that you don't trust her.
Your 13yo needs you to rebuild her trust in you. She did tell you there was a problem, and she needs you to tell her that she did the right thing by speaking up. She needs to know that you couldn't hear her then, but you're listening now, and then let her talk.
You need eyes on supervision of your 3yo, which means your 3yo is in sight of an adult 24/7 with the adult watching over her. The 3yo is vulnerable and this is how you keep her safe.
To actually keep your 3yo safe, you must have eyes on her every minute of every day from now on, until a future time when your 10yo has recovered and regained your trust. There are no quick fixes for this, so eyes on supervision may need to continue for a while.
If you really cannot make your home safe for everyone living together, then you'll have to make some tough choices. For example, maybe you and your husband have to live apart for a while, where the 13yo and 3yo live with you, and the 10yo lives with him.
A home has to be safe for everyone, and when a home is not, then something has to change.