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Well, there is the traditional saying, Semel Catholicus, semper Catholicus, once Catholic, always Catholic. So when she was baptized Catholic, she remains validly baptized as a Catholic. Of course, when she officially passes to a heretical or schismatical community and then returns to the Church, she must again make the profession of faith and reject the errors, heresies, and schisms when she, or he, joins again in the practice of the Catholic faith.
In the case of marriage, this person must have the permission of the bishop to marry a non-Catholic, or a dispensation from the form when there is only a civil marriage. I think in this case it would be invalid without the permission of the Church.