This girl needs serious help. Psychologically speaking, by loving a priest she is coming closer to God.  This is on an unconscious level.  She may also see the priest as her "Good Father" if she has had a difficult or abusive realionship with her own father.  From the beginning of Christianity there have been sexually inappropriate priests so one must be very careful about trustworthiness.  Sexual fantasies are normal; just don't act on them.  The priest has all the power if he goes along with you.