I have a 13 yr old daughter. she is very thin and weak. she gets severe headache if she skips a meal. can she keep rozas.

May Allah grant her good health long life. Aameen
But as per the ruling she has to fast only she can skip when it is such kind of the disease which restrict her to fast. She may take her medicine at night time.
If still not possible then she may travel only this is the way she may skip and thereafter she will do the qadha in winter or anytime during the year when it is convenient for her but she has to complete 30 days before next Ramadhan Ul Mubarak
Syed Abul Qasim Rizvi