All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
If a fasting person intended to break his fast and was firm in this determination, his fasting is definitely invalidated by this. However, scholars differed concerning suspending the intention upon the presence of treatment as to whether it invalidates fasting or not.
Ibn Qudaamah said in Al-Mughni: "If one intended that, if he finds food, he would break his fast and that, if he did not find any, he would complete his fast, then there are two opinions from scholars concerning this. The first is that this invalidates fasting because he did not keep firm in his intention to fast. Moreover, one may not start his fasting with such an intention. The second is that he continues to fast because he did not have a complete intention to break his fast. Intentions may not be suspended on a condition. That is why no fasting is not valid with such an intention.”
The opinion of invalidating the fast was held Saheeh by Al-Mardaawi in Al-Insaaf ;he said: "According to our school (the Hanbali), if one hesitated in breaking his fast and intended that he would break it later or said, ‘if I find food, I will eat or, otherwise, I would complete my fast,’ then. It was said that it invalidates fasting because he was not firm in his intention. Al-Athram reported that this does not avail him of the obligation until he is determined to fast the entire day. I said: ‘This is correct’.”
If the sister who posed the question repeats fasting this day to be on the safe side, this will be better for her in order to free her of any liabilities and to be safer for her religion.
Allaah Knows best.