There is little evidence that cognitive behavior therapy (CBT) is helpful for young children with ADHD, but it may be effective for adolescents. CBT works best for adults with ADHD; in some cases, it is as effective as medication. CBT works especially well in tamping down anxiety. If your daughter seems anxious, as do many children with ADHD, this would be an additional reason to consider CBT.
In deciding whether or not to seek therapy for ADHD, focus on what behavior, or pattern of behavior, you are trying to change. If she has organizational problems, like getting homework done or remembering assignments, an ADHD coach would be a better solution. For major oppositional problems, look into parent training programs. The Nurtured Heart Approach and Parent Effectiveness Training, with or without therapy, are good ones.
The skill and empathy of the CBT therapist are important to successful treatment. Ask fellow parents for recommendations of a practitioner who helped their child.