This page at the website of the National Office for Vocation includes a paragraph indicating the origins and the juridical standing of the vocation of the consecrated virgin in the Church. A more detailed explanation of the vocation to consecrated virginity, as lived in the life of the Church of our own times, can be found here: Consecrated Virginity in the World. What is it? This post describes an experience of the Rite of Consecration itself: 'Sponsa Christi' on Consecrated Virginity.
Consecrated virginity, appears then, to be distinctive in comparison to consecrated life in general for two reasons. It first of all consecrates a state of life already existing. It requires the woman consecrated to have lived a life of virginity even before her consecration. This appears not to expect a conversion of life that might be characteristic of consecrated life in general - though I would expect that that conversion has occurred at some point in the time before consecration. And secondly, it is the prayer of consecration that constitutes the effective feature, and not the promises or vows made by the recipient of the consecration. The woman is consecrated, rather than making an act of consecration themselves. This creates a state of life from which the Church is not able to grant a dispensation. (There is a certain analogy to priestly ordination here, where the promises of obedience and celibacy are not of the essential form of conferral of the sacrament, and the sacrament confers a permanent character.)
That this form of life existed in the Church before that of religious life, and the consecration associated with religious life, is thought provoking. Does it perhaps, because of its indissoluble character, represent a fuller actualisation of a notion of "spiritual marriage" than do the vows of consecrated life in general?