It has not deviated from the original track. Adultry is only if there is a legally sustainable marriage. If the man is not legally married, he is not guilty of adultry. So the question of validity of marriage is relevant.
Secondy,she wants to get out the relationship with the guy and sought advice. From the wordings of her query, it appears that she is not married legally. If that be the case why go for complicated procedure for divorce?
The best course for her is to assert that there is no subsisting marriage and ask for divorce only if he proves otherwise. Especially since her apprehension is based on what seems to be just a notorised agreement that does not constitute legal marriage.