In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
2- As for what has passed of her prayers, she does not have to repeat them.
Answering your question, the late Saudi scholar, Sheikh Ibn Baz (may Allah have mercy on him) stated:
If she does not see any of them, then the strongest opinion among the statements of the scholars is that she does not follow the Imam in the prayer. As for what has passed of her prayers, she does not have to repeat them, Allah willing, because there is no clear evidence that they are invalid prayers. This question is an area of ijtehad [juristic reasoning] by the scholars. The safest and strongest opinion is as we have mentioned.
Almighty Allah knows best.
Source: Islamic Fatawa Regarding Women, Compiled by Muhammad Ibn Abdul-Aziz Al-Musnad and translated by Jamal Al-Din Zarabozo, Darussalam, 1996.