Dear Sherry,  

Most religious congregations do a psychological evaluation of their candidates using the services of a professional psychologist. They usually make sure that the psychologist understands the nature of religious vocation and the workings of grace, since otherwise he won't have all the elements needed to come to his conclusions. It is not just a question of having "psychological health" in general, but of having a psychology that with the help of grace is a good basis for the religious commitment.

God bless.

-Fr Anthony