5 year old dark circles under eyes

So my daughter is 5 and autistic. She is super high energy and has a pretty limited diet(despite constant efforts to expand it). The last 6 months or so I have noticed some dark circles under her eyes that start out fairly normal in the morning but seem to worsen as the day goes on as well as beginning to rub her eye area. She doesn’t have any apparent signs of allergies(we live in the dry desert) and plays pretty normally although I have noticed her wanting to sit/lie down and relax more. I will also note she is fair skinned and always has been. l I took her to the doctor for it a couple months ago and he said the circles weren’t bad and checked her iron which was fine so he chalked it up to her complexion. My anxiety is driving me nuts over what it could be and she has another doctor appointment Friday where I’ll ask for labs for a full check-as well as an eye appointment next week. Anyone gone through something similar though? I’m a big ball of worry rn thinking the worst case stuff like cancer. 😫