I feel for both of you. Its the end of the day and you are both tired. And since it is closer to her bedtime, she is probably just barely hanging on. So things are going to happen. Avoiding "triggers" is the first line of defense.
Specialmom has a lot of great ideas. I wrote a very long post awhile back to a parent with an 8 year old girl with adhd who had similar problems. So I am going to quote part of that post (I spent a lot of time on medication which I don't think yet is a problem). I think you will find a lot of helpful info. Here it is........
So, after all of that. What if its not the meds or the meds are only part of the problem. Kids with ADHD have tons of anxiety and frustration and anger. It comes with the ADHD. They need to be taught how to handle this. I know you said she was going to counseling and her psyc - but are you also there? All the good stuff they tell her has to be practiced at home. An 8 year old cannot hear something and decide to do it. It takes practice. It takes a parent who can help her notice when anger is coming on and clue her in on dealing with it - before it overcomes her. I have some very good links on dealing with anger.
The first link is from our Child Behavior forum. Even though it is aimed at a 4 year old the techniques are simple and very good. The first answer by Specialmom is the main one to read. She has many, many good ideas. But the other answers are also worth looking over. I will give you two more links on anger - but I like this because the others are a bit technical and this is very practical.
The link is :
http://www.medhelp.org/posts/Child-Behavior/4-year-old-son/show/2423496
The second link is from CHADD and is a bit technical, but really covers and explains the whole anger management thing. I think you will find it dovetails nicely with the above link. it is:http://www.chadd.org/Portals/0/AM/Images/Understading/AUG01AngerOverloadinChildren-DiagnosticandTreatmentIssues.pdf
And the final link is from one of my favorite places for ADHD information. Feel free to click on the topics at the top of the page for lots more info. This link is kind of an easy overall look at what the first two said in detail. It is: http://www.additudemag.com/slideshow/42/slide-1.html
Finally, the books I mentioned in the first link were aimed at the 4 to 7 year old crowd. There is another set aimed at slightly older kids. There are a couple sets of books aimed at this age group. One is, " How to Take the Grrrr Out of Anger" (Laugh And Learn). That and several more are found here - http://www.amazon.com/Take-Grrrr-Anger-Laugh-Learn/dp/1575421178/ref=pd_sim_b_7
Another good set is the," Don't Rant and Rave on Wednesdays!" The Children's Anger-Control Book. That and others in the set are found here - http://www.amazon.com/Dont-Rant-Rave-Wednesdays-Anger-Control/dp/0933849540/ref=pd_sim_b_1