What Order did the Nuns belong to?

I don't think they're supposed to be identified with an specific order, so I think the habit just has a generic "nunnish" look.

They adopted the habits of the French order known as the Daughters of Charity, of St Vincent de Paul. They wore a cornette, and a blue scapular. I believe this is even mentioned in the book the tv series is based upon, but never was this order mentioned in the series.