"μωρή" is the feminine gender of the adjective μωρός, μωρή, μωρό.
“μωρός” means immature (ανώριμος) or idiot.
See here for a full discussion of μωρός and βρε.
"Μωρή" is used when someone talks with great disrespect to a woman, in order to express anger. It is very impolite.
In modern Greek it is only used in vocative case form:
Μωρή, τι είναι αυτό που έκανες; Πέταξες τα ρούχα μου;
You idiot, what did you do? You have thrown my clothes away?