Go Art Therapy!
I'm a registered art therapist and licensed clinical counselor. Sigh, your dd has chosen a tough path - rewarding but tough. I don't have ADHD but can sympthasize somewhat as I have a very strong "spontaneous" disposition due to my artist-side (or I always blamed in on being left-handed).
I think JohnLaw's question is paramount: does she understand that this is not only working for her in the present, but will not work for her in the future?
I would be happy to answer any of your or dd's questions if you want to PM me. Here's a few thoughts I have off the top of my head. First off, most art therapy master's programs are highly competetive (though there was less choice when I went 17 years ago...eek). That is because most programs are highly selective and only take about 10-20 students per year. The program I was in was for dual art therapy and also clinical counseling (for licensing purposes) and only took 8 full-time students a year. I chose my program because it had a many opportunities for scholarships and assistantships. Master's degrees (especially from some of the elite schools that offer art therapy) are TOUGH to pay for on a $30K/year starting social service salary (and that's if you're lucky...double sigh). I was fortunate that my schooling was paid for (including a stipend) my first year. That being said: she needs to get serious about her academics (especially her psychology classes). Not that the fine arts classes don't matter...but all B's in pyschology won't cut it. In the long run, an art therapist (while needing to have an understanding of the art process, materials, and how art can create change in a person) is a clinician. We are expected to diagnose, work as independent clinicians, and become licensed (differs by state).
That being said, I would highly HIGHLY recommend that she do some volunteer work (if she is not required to do internships or practicums for her bachelors) where she gets a sense of working with different client populations, gain clinical experience, and even determine if this is a right fit for for her. Additionally, masters programs will want her to have hands-on experience with kids, adults and senoirs.
Lastly, I cannot emphasize how important it is for a therapist to go through their own therapy. I did not enter into therapy until my master's program (we were required), but I wish I would've even started earlier. As a student, I received free counseling from my college counseling center (I requested a working professional - not a master's level student) with an excellent psychologist. He was not an art therapist, but was very open to me bringing in my artwork/writing. It was through therapy that I saw the personal flaws that would affect me personally and professionally, and also worked through issues that would've become stumbling blocks for me as a therapist attmempting to help others.
What an asset your dd can use when applying for graduate school: that she faced her challenges head on and has first-hand experience that she can share with her future clients.