My 10 years old step daughter is forgetful

She could have ADHD. My daughter does not have the hyperactivity as much as others do but her attention is awful. It can be very frustrating for both the child and the parent. She is almost 15 and she still can walk from one room to the other and forget what she was supposed to do. Only telling her one thing at a time works best. The littest thing can distract her if she does have ADHD. A tv, a bird outside.. anything. I know it drives her dad nuts because he forgets and gets so upset when he tells her to do something and 5 minutes later she has forgotten. She isn't doing it to be bad she just seriously doesn't remember. I would talk to a doctor and see if this might be the case for your step daughter. The knowledge doesn't make it easier just understandable.