Thank you for your query.
If your daughter is gaining weight and her thyroid
is normal then you need to sit down with your doctor and do an audit of her meals. Once you write down what she has during a 24-48 hour period, the doctor shall be able to guide you what needs to be reduced or modified in the diet so that your daughter does not gain weight more than recommended for her age group.
As regards the peppermint smell of your daugher's hair and urine, it shall be advisable to get an examination of urine routine and for reducing substances and discuss with your doctor.
I hope I have answered your query to your satisfaction.
Wishing your daughter all the best.