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.