What medication is she currently on?

Btw, if you curious, this is what I currently take.
[Stimulant]D-Amphetamine/Salt Combo(Generic of Adderall) 30mg x2 a Day
[Anti-Depressant*]Bupropion(Generic of Wellbutrin) 150mg x2 a Day
[Anti-Anxiety]Sertraline(Generic of Zoloft) 100mg x1 a Day

*(It's the favored Anti-Depressant for people with ADD/ADHD, for whatever reason it seems to have a stronger response than other Anti-Depressants.)

As for advice for school... I'm not really certain how to answer. Even today I'm still trying to address things that are still issues for me. Medication has definitely helped, but it doesn't take care of it completely. It does help manage the symptoms, but you tend to still have a bit of a handicap when it comes to mental energy for the day.
One of my biggest problems was finishing homework... its why I was typically a C or D student. It's not that I couldn't understand it... its just I had trouble processing information during class and when I got home I always felt burnt out and always wanted to do TV or Video Games because it allowed me to decompress.
If you believe in the IQ system, according to the test I'm quite intelligent. I scored 140. (90-100 is average, 160+ is genius.) Granted this test should be taken with a grain of salt...
The example metaphor I use for myself is this: "My brain is like a nice computer... but 50-60% of the CPU is being used for absolutely no reason. Which causes it to be sluggish."

Again I apologize for rambling so much, lol.

I suppose the main things would just be to have patience with her and always be supportive.
A dairy/journal can be helpful so she can put down her thoughts so it may stop looping in her head as much.
I'm a little bit of a skeptic of taking the routine/schedule approach. I mean it's fine to outline like a general idea of the day... but like doing it like to the hour or minute is a little too severe in my opinion. The repetitiveness can easily induce boredom and may even hurt her esteem or have feelings of inferiority because some one has to plan for her. Again lack of control can be a terrible feeling.

But like I said, that's just my opinion. Obviously different methods work for different people. There's really no cookie cutter solution.

EDIT: I suppose the biggest thing is to let her know that her disorder doesn't define her life. If you keep thinking because of it you'll never be happy or successful or normal... you'll start to believe it if you let it long enough. Just let her know that her ADHD doesn't run her life, it's just along for the ride.