How was Queen Keran, wife of Leo II of Armenia, able to become a nun? Queen Keran (or Kir-Ann, d.1285) bore her husband Leo II (d.1289) fifteen or sixteen children. By all accounts, she was a loyal and devoted wife. This article on http://enacademic.com/ states:


  Many words of praise were made about Queen Keran by her contemporaries. Her son Hethum claimed that "she had a wonderful soul and a beautiful body." The chronicler and scribe Avetis, described her as "a good friend to her husband in trouble and joy."


However, after the birth of her last child in 1283 or 1284, she became a nun at the Drazark monastery (Armenian Apostolic Church). I haven't been able to find any information on this relating to the medieval period.

Were married women able to become nuns in the Armenian Apostolic Church in medieval times?
While not specific to Queen Keran's situation, this section from Medievel English Nunneries 1 may provide some clues.

Motives for taking the veil: a refuge for widows and occasionally for wives. 


  The occasional cases in which wives left their husbands to enter a
  convent were less likely to provoke discord. Such women as left
  husband and children to take the veil must have been moved by a very
  strong vocation for religion, or else by excessive weariness.


After fifteen or sixteen children (three pairs of twins!), who could fault Queen Keran for claiming excessive weariness?


  It was necessary for a wife to obtain her husband’s permission before
  she could take the veil, since her action entailed celibacy on his
  part also, during her lifetime. Sometimes a husband would endow his
  wife liberally on her entry into the house which she had selected.




1. Medieval English Nunneries c. 1275 to 1535 by Eileen Edna Power, Section 5b (Cambridge At The University Press, 1922)