Rereading this, I notice that it feels more like less of an Incest story so much as an Age Gap story, if that makes any sense. The niece isn't angsting at all over that fact that it's her aunt she's in love with - that aspect of their relationship is only mentioned at the very beginning and isn't brought up again. Of course, this could change over the course of the story.
This isn't really a criticism or anything, just an observation.