The suggestion of 'sinful women' is not conclusive. It stems from the use of the latin word meretrix which at the time of the founding of Fontrevaud by Robert d'Arbrissel may or may not have meant prostitute. The relationship to prostitution may stem from d'Abrissel's supposed visiting of houses of prostitution and leading the women away from that life. Some of this seems apocryphal, including allusions to Mary of Magdalene; so much of his life is obscured by convenient, allegorical legend.

Leaving aside the discussion of meretrix, the abbey quickly became a locus of charity by the ancestors of Eleanor of Aquitaine, establishing its relationship to Plantagenet nobility in perpetuity. It comes as no surprise that in the 12th century nobility is attracted to the 'selflessness' and 'self-abnegation' of religious mystics who are invested in saving those on the margins of society like prostitutes and lepers, it was very common. The question we still wrestle with is what made this an attractive proposition? I would be speculating if I offered an answer on the relationship of sin and nobility.

For discussion of the use of meretrix in the high middle ages, see the introduction to Leah Lydia Otis, Prostitution in Medieval Society: The History of an Urban Institution in Languedoc (University of Chicago Press, 1985)