I also posted on the ADHD forum, but just in case you are only checking one - here is a copy.
First, her meds probably are not working in the morning. Depending on the med it can take from 20 to 60 minutes to began working.
Kids with ADHD and not on meds do things without thinking. Find a lighter, play with it, without thinking twice about it. And, obviously, there is no way a lighter should be accessible to her or any of your kids!
To punish a child with ADHD who did something without thinking is a waste of time, because they still won't think twice the second time (at least not till they are a lot older). And by now the punishment or your attempt to change the behavior is too late. Any attempts at punishment or behavioral change has to be immediate (and consistent).
I think that at least until she is somewhat older you will have to keep an eye on her.
The school thing could have just been a bad day for her. Kids got her ticked off or something and the teacher was just reporting what happened.
Or it could be that her meds are wearing off or she has gotten used to them. In which case you need to talk with her doctor. Its an easy thing to fix. And, he could also possible make sure they last a bit longer in the day.
The thing that YOU need to do is to make sure that you understand how ADHD works and how it effects kids. It really involves more than just taking a pill. Your questions show that for at least some part of the condition of your child, someone has not given you much information.
I suggest you buy the book, "The ADD/ ADHD Answer book," by Susan Ashley. Its about $10 on Amazon. It will help you a lot!!!! It also will give you good ideas on discipline, how to help the schools help her, etc.
And, if you have any more questions, please don't hesitate to post. Best wishes.
As much as I hesitate to advise parents to take their children to a psychiatrist or psychologist, this is time to go to general quarters. Secure all matches and lighters in the house, make sure there is nothing exceptionally flammable in her room, purchase carbon monoxide and smoke detectors for every room in the house, keep a close watch, and seek professional advice and consultation.