In American Horror Story Season 1: Murder House, why does the spirit of Moira (the maid) not appear as her younger version (by default, anyway)?

I recall early on in the season the whole "men see what they want to see" idea and how they would obviously want to use that with Ben, but none of the other spirits ever seem to age, as the original owners still appear as they did when they died.

Later on, Ben even comes to see Moira as her older self. But is she putting in a conscious effort to appear old all of the time now? It seems as though she just wants to appear as her older self, although I don't remember this being explained at all.