Girl

You don’t need to mention you past sins to any one but Allah Who is The only Forgiver. Disclosing your past sins to other than your Creator can harm you. Keep seeking forgiveness and pardon from Allah (SWT).

Wassalam.

Sunni Shaikh can recite the Nikah because it is after all a Nikah contract recited by either Shia or Sunni or any one who knows Arabic properly.

The main point is to be sure that she will remain in the future respecting Ahlul Bayt (AS) and will teach your children the teachings of Ahlul Bayt (AS). You are responsible about the future if your children.

Wassalam.

Wali of virgin girl is her real father or her paternal grand father. No one else can be Wali for virgin girl. If the father opposes a marriage with a comparable Momin for no valid reason, and the girl needs the marriage to protect herself from sin, then she can refer to her Marje' of Taqleed to seek his verdict in such situation.

'Wassalam.

Father is not allowed to reject his daughter's marriage with a compatible believer when she wants to save herself from sin, just because of a cultural reason which is never a condition in Sharia.

I advise her to contact her Marje’ of Taqleed to explain to him his situation and seek him guidance.

You can get the email address of the main Maraaje’ of Taqleed in the Internet.

Wassalam.

Yes if the girl is virgin which means that she was never married.

'Wassalam.

You need to take them to an authentic scholar who can explain for the the Islamic rules according to Ahlul Bayt (AS) and tell them that following Ahlul Bayt (AS) is much more important than following the culture or society.

‘Wassalam.

If the virgin girl has no living father but has a paternal grand father, his permission or approval will be enough. If she has no living father nor paternal grand father, then she can decide herself for herself and does not need a permission from other family members.

'Wassalam.

Marriage between Muslims from any Islamic sect is permissible in principle, but if you know that this marriage can harm your faith or religious practice, then you should avoid it because saving your faith and religious practice is more important than marriage. Your mother's happiness can not be through endangering your future. You should explain to her in suitable and polite way your situation and never allow such forced marriage if you feel that it can harm your faith or religious practice.

'Wassalam.