Well, Seadragon, I don't know how subtle this writing is, without some context. All we've been given is one sentence to explain. The 'translation' I've given is the only obvious one, the one a native English speaker would give.
If the author has been away from her own house for a long time, or she has been prevented from living in it, and it was no longer her home, perhaps because someone else has been living in it, and she the returns to it ,to have it as her home again, then she could be 'making herself at home in her house'. However, if that was the story I'd expect the writer to put 'The author makes herself at home in her own house' to make it clear , and emphasise that the house is her house and now she is making it her home, treating it as her home .
One could envisage such a case. 'A house is not a home' we say. She could be , in her mind, claiming tne buliding, her house, as her home, thinking and asserting by her conduct that she is making herself 'at home' in it.