In the Motu Proprio Ecclesiae Sanctae of 1966, implementing various decrees of Vatican II, Pope Paul VI said:
Although Religious who recite a duly approved Little Office perform the public prayer of the Church (cf. Constitution Sacrosanctum Concilium, No. 98), it is nevertheless recommended to the institutes that in place of the Little Office they adopt the Divine Office either in part or in whole so that they may participate more intimately in the liturgical life of the Church. (n.20)The relevant part of Sacrosanctum Concilium 98 says:
They too perform the public prayer of the Church who, in virtue of their constitutions, recite any short office, provided this is drawn up after the pattern of the divine office and is duly approved.My correspondent points out that therefore the Little Office remains part of the public worship of the Church. As it was never officially revised following the Council (although some institutes have unofficially revised their own version), it would seem that in this case, the older form of the Office is the Ordinary Form, and, contrary to popular belief, Prime is still part of the Ordinary Form liturgical worship of the Church, as the Little Office contains Prime!
It is worth noting too, that although Vatican II spoke of a "short office", the Little Office of Our Lady is substantially longer than the Liturgia Horarum. I think that the Little Office of Our Lady is becoming more popular among the laity, and it can be readily obtained from various outlets, for example Southwell Books.