If your daughter has had NO exposure to ghosts through TV, vivid halloween displays in the neighborhood, books, movies, etc., I'd say maybe you have a ghost. If there was any place she may have learned of ghosts, it may be her imagination, either way, it is scary for her.
My parents have a very old house, with lots of rumors of ghosts. My sister-in-law thinks my 2 year old niece saw one at Thanksgiving. (personally, I never did, but one of my brothers may have)
I think you have good advice with the monster spray (again, especially if she has had any exposure with cartoons, christmas specials, halloween specials, etc.). Also, leave a night light on in her room, but while you don't want it to be too bright, make sure it's not somewhere that it casts scary shadows either.
The only other thing is, what did the priest use to bless the house? Was it holy water, or did he use something to sweep out evil spirits? Santoria, for example, uses mercury. they sprinkle it on the door threshold and sweep it out of the house, to sweep the evil out. they also sprinkle it in babies' cribs. Mercury causes mad hatters disease, which makes you act "crazy as a mad hatter" (mad becuase they used mercury in the hat making process and it made them act crazy) Just making sure there is not an environmental component.
Kids have fears, they have imaginary friends, and they may see ghosts (real or imagined). I would do what you can ahead of time to try to ward off the ghost, and then comfort her just as you would if she had a nightmare when it happens. If it continues to happen, but only in her room, you could try setting up a different area of the house for her to sleep in (if you have the space). Good luck!