(2) Few days ago she told me that for months after she became Hanafi she used not to wash mouth & nose in ghusl but she doesn’t remember how many months. Should she repeat her prayers? If anything else needs repeat or do please mention it.
(3) Second thing is she used to pray sunnah muwakkidah and witr salah sitting on ground while on Shafai madhhab, so when she became Hanafi she continued praying sunnah & witr sitting, when I told her it is not allowed sitting she stopped praying sunnah muwakkidah at all for months, but now she is back to praying sunnah & witr but sitting down.
(4) Should I stop her again from doing so? I am afraid she would stop sunnah again. I am confused, please advise me what to do.
بسم الله الرحمن الرحيم
(1) What forced your wife to change her madhhab?
(2) If she did not put water in her nose and mouth then ghusl was not valid. Whatsoever salah she offered with this incomplete ghusl without making wudhu all were invalid. Now estimate how many salah she might have offered in this state she should offer that much salah again. However, those salah will be valid which she offered after making wudhu though after passing a long time of ghusl and while doing the wudhu she entered water in her nose and mouth or she gargled without wudhu and entered water in the nose and then offered salah in the state of wudhu.
(3) She should also reoffer all those Fajr sunnah and Witr salah which she offered in sitting position without a Shariah excuse. However, there is no problem if she does not reoffer sunnah muwakkidah salah.
(4) Keep on convincing your wife with wisdom and politeness. However, it would be better if your wife reads Bahishti Zewar, Talimul Islam, Tohafa-e-Khawateen (written by Maulana Mufti Muhammad Ashique Ilahi Sahib Bulandshahri RA) or you read it before her.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.