Well it sounds like you are doing a great job, the living situation is genius by the way. I know some times biological differences can cause the biological child added emotions even if the adopted child has been around forever. I would try to dig deeper into having her elaborate her feelings a little more. Or it may be that she is directing controlling behavior towards your son because, she feels that she is lacking control in other areas of her life and may feel that by being controlling towards her brother is a way for her to regain some control in some way, you did mention that she won't get a job because, she is fearful of the interviews, and will not file for disability because, she has a hard time understanding the questions and also that she will not allow you to help her. She may want to have her independence but it also sounds like she is fearful of rejection or failure in some way and may be feeling like she has no control of her life. Trying to figure out if her controlling behavior worsened after school or around certain time frames may help. Or asking her questions bluntly and gently. You can only help her if you know what is going on in her mind. Unfortunately you can only find out if she communicates it to you.
I hope it all gets figured out and that things get better and I hope I was some help to you. Stay strong, your doing awesome!

Have you asked her why she feels the way she does? It may be a jealously issue, even though she is older she may feel that he is getting more attention than her because, he has additional needs (I am positive that you do not neglect your kids) but sometimes they can feel left out or feel that their wants and needs aren't being met because, of their siblings needs. Is your 24yr old adopted as well or biological? There are several factors that could play into this depending on that. I would get into more detail with her about what he has been through and specify their differences as well as the differences that everyone has. No two people are the same. Let her know that she is an important person in his life and that he loves her and looks up to her as a big sister and that he needs encouragement and guidance just as she did. Try to spend some one on one time together with her if at all possible and then try to do things together with you, her and your 7yr old that you think they would both equally enjoy so they can share in something that they have in common.

I am terribly sorry to hear about what your son went through as a baby, it is fantastic that he is with such a loving, and devoted parent. :)

Thank you everyone! Ashley (Phone number can only be seen by the question and answer creators) my daughter is my biological child. My son looks up to my daughter so much, but lately even he has asked me why his sister is always yelling at me and telling me what to do. I tell him its because she loves him so much so wants to be sure he is being taken care of right. We have a house rule that we spend at least 1 hour and 1 meal together every day and we do it on her side of the house. ( My house is a roommate house it has a bedroom (s),bathroom, and livingroom on each side with a shared kitchen. I chose this house so my daughter could still have her own "apartment" and be self sufficient but I am still there if she needs assistance).
I guess all I can do is keep trying to help her see.