I'm glad you mention she already has an IEP. What I would suggest now is to bring it up at the next IEP meeting (or even, if it's a ways out, request to talk to the IEP team, even briefly). Tell them about how artistic she is and how well she focuses, so they can start looking for a way to use this love and skill to reach her and teach her.
This is a classic marker of ADHD, by the way. Complete lack of focus and attention on some topics and circumstances, and hyper-focus on others. Being able to identify and build the areas of a child's strengths is important for every child, but especially for one with ADHD. They hear so often how they are lacking in school skills and how they need to work harder; it's good for them to hear just as much about what they are good at. And you can specifically point out how well she focuses on these things. Build her self-esteem. And the more she hears that she is good, from you and the school, the better she gets - in more areas.
Like I mentioned, the school should teach to her strengths. She may not love numbers or letters, but if, at least part of the day, the teacher can teach things in a way that she can express them artistically, it will benefit not only her but every child in the class. And in pre-K and Kindergarten, there should be plenty of opportunities for kids to be creative and artistic; it should not be all drill and such.
I will be honest - school will probably be a struggle for her all the way through (I taught a couple of kids with ADHD, as well as watched my brother, and now my son, go through the school system - there will not be any shortage of challenges) so she will need your help and support. Be her biggest cheerleader, but also be firm and require that she spend a few minutes a day on "homework" (playing games with letter and numbers is good for now). As she gets older, expect that homework may likely take her longer than for other kids, and that you will need to sit with her as she does it. But as she gets older, she also will mature emotionally, and be able to see that there is a need to try to focus and go along with what the class is doing.
In the mean time, enjoy her independence and creativity - and let her build on those!