If the parents are frum, talk to their rabbi. Almost by definition, a frum family is more concerned about the frumkeit of a prospective son-in-law than any other factor. Halacha says you can disregard them (i.e. “elope” most probably), but their rabbi might persuade them to be cooperative.
If her family isn’t frum, ignore them and elope (they will be angrier about her becoming frum than what the grandchildren look like).