Also, do you know any good techniques for managing the behavior of ADHD? I feel bad when I punish her all the time, yet in some instances she really couldn't help it. She's failing first grade and I'm dealing with a lot of "I've failed as a parent"-type issues.
You're right about punishing your daughter for things she can't seem to help. You need to say to her, "Honey, I know that (the right thing) is hard for you. You get excited and sometimes you forget. What do you need to do to make (the right thing) happen?" Getting her to self-monitor (think about what she did) and come up with the proper behavior will be gifts that your daughter (and her teachers) will value.
Here's what I'd suggest about keeping the room neat: Make a list of the things that you would like to have her do to keep her room neat (keep it simple, with only three or four tasks). To get her involved, ask her to pick just one thing that she is capable of --not necessarily willing -- doing. Then come up with a list of things -- she should help you generate this -- that would be good "rewards" for her. This doesn't need to be a list of expensive items, like CDs or dolls. This list should include activities that are no-cost or low-cost, and that have some other benefit (like being read to by you, watching a TV show with you, or making or baking something).
Then ask her how many nights she thinks she can do the deed you picked. If she says something unreasonable, such as "forever," then you suggest something more reasonable, like five out of seven nights this week. Make a chart on which you can put a star or sticker for every night she does the desired task. Do this at the same time each night and try to do it when your little girl is relaxed (after listening to some calming music or after her bath). Sit in the room and watch her do the deed (not to hover over her, but to be there to notice and to make positive comments).
This activity should seem fun and pleasant, and even if it may only take a couple of minutes, this can be the start of a much larger program. If she reaches her goal, she gets the "prize" you have agreed upon. She may be one of those kids with ADHD who just can't wait until the end of the week to get the reinforcement. In that case, you might want to give her a token (a penny, a poker chip, or a playing card) each night that she does do the task and let her watch these add up.
Some people call this approach "bribery." I think it's a wise use of positive reinforcement to help a child learn better skills. Remember that kids with ADHD don't pick up these tasks easily; they have to learn how to do them. This method is positive and helps build skills one at a time. As she gets good at this skill, pick another task to work on next. Keep reinforcing the first skill, but slowly phase out the rewards over time.
What I've described sounds easy, but it's actually hard to do consistently. You may need the help of a psychologist or social worker to make it work. Ask the teachers at school for a recommendation. Finally, since your daughter is failing first grade, please make sure that she has a very thorough evaluation to make sure she doesn't have any learning disabilities. These problems often go hand-in-hand with ADHD and may be making school very challenging for her, as well as creating some behaviors that may just appear to be part of the ADHD.
If you can, take a class for parents of kids with ADHD that's given through the school or some community agency. You won't regret it. Hang in there!