If your father has passed away I would assume that the house is now in your name and she cannot sell.
If you father has passed away the reason you cannot find his will is because it was given to the court and you will have to contact the supreme court and ask for an exemplification of the probate that was granted.
If your father is still alive and then house is in his name your mother cannot sell it unless he agrees.
Until he passes the house is not yours.
You should also contact the solicitor that prepared the wills they may have copies.
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