How frustrating for you, and especially for her. It sounds like she just doesn't know how to deal with and express feelings. Just as a suggestion, and it may not seem like it's related, but you might want to focus on what she's eating. Red and yellow food dyes, chemical preservatives, etc. in processed foods really can have an effect on children's as well as adults' behaviors.
I have a friend who saw amazing changes in her child's behavior (angry, tantrums, hitting, etc.) after she removed red and yellow food dyes from her diet. Then a week later, when her child accidentally had some colored candy, all the anger and hitting and tantrums came right back for the next couple of days. The proof was in the pudding, so to speak.
As I said, it may seem disconnected, but it's definitely worth a try, if it might work, especially since it can't hurt. And if she knows you're doing something to try to help her because you love her and don't want her to be frustrated, then she knows (even if she doesn't always act so) that you love her and just want to help her.
Peace and best wishes,
K.