As a girl who does not wear a hijab, does that invalidate my fasting in Ramadan?

The fast of a woman who does not wear hijab (definition) is valid, because abandoning the hijab is a sin that does not invalidate the fast, but it diminishes its reward. Fasting is not merely abstaining from food and drink; rather, it is abstaining from unlawful acts, and refraining from idle talk and obscenities. Therefore, a Muslim woman should make her fast a motivation for her to obey Allah and distance herself from His prohibitions, and that includes adhering to the hijab.