If so, it may well be that she has an anxiety disorder alongside her ADHD
. This will require further evaluation
by her menatl health providers. Some of the ADHD medications can exacerbate anxiety, so it's a variable that needs to be considered in treating the ADHD. If it looks like either (a) her medication may cause the chewing, or (b) the medication is exacerbating her anxiety, it would be sensible to switch to a non-stimulant treatment (such as Strattera) for the ADHD.