Yes, the young lady was in the convent of her own free will.
Just imagine that you decided of your own free will to become a sedevacantist, or SSPX, or even FSSP ... and your family were dead set against it, and so declared it a cult, even though you had made the decision freely, and they come and kidnap you, subjecting you to deprogramming, which was in this case actually programming, where by deprogramming you're programming the person to believe that she had been programmed in the first place. Now, one could make the claim that SSPV have some cult-LIKE tendencies, in imposing some of their opinions on people under pain of excommuncation (being refused the Sacraments), but they're not a cult who program people into sedevacantism. To this day they have no problem with the faithful at their chapels to also assis at SSPX "una cuм" Masses.