No, she does not need to make up what she has already performed when she was a Sunni. All worships performed according to her previous sect does not need to be repeated.
This question comes in performing every religious duty on us as we need to be sure that we do it the correct way. The way to be sure that you follow the most authentic narrations and most authentic Islamic divine leaders among all the different narrations and different leaders. Sunni sects follow Abu Hanifa or Al-Shafi’ or Malik or Ibn Hanbal or Ibn Taymiyyah. Nine of them ever met the Prophet Muhammad or heard from him as all of them were born long after the demise of the Prophet Muhammad (SAWA). Shia Muslims follow the divine leaders from Ahlul Bayt (AS) who lived with the Prophet and narrated the real Sunnah of the Prophet and the real Tafseer of Quranic verses. Following Ahlul Bayt (AS) means following the Prophetic Islam.
Shia man is allowed to marry a Muslim woman from any Muslim sect as far as such marriage will not harm his faith and religious practice. If your mother is disagreeing, then you need to do everything you can to convince her and make agree without forcing her. You should never cause anything which hurts the respect or the feeling of your parents.
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