Is the fast of my sister, who drank because she thought the dawn had not yet broken, valid, and what are the implications?

If a person eats while in doubt about the dawn breaking, and it does not become clear to him that he ate after the dawn broke, then his fast is valid. This was stipulated by Ahmad, and it is the opinion of Ibn Abbas, Ata', Al-Awza'i, Al-Shafi'i, and the jurists of opinion. Its meaning was also narrated from Abu Bakr Al-Siddiq and Ibn Umar. Therefore, your sister's fast is valid, and you must make up for the day you broke your fast due to doubt. As for fasting on Friday, she does not have to make it up.