Why does the author of Eveline uses unusual sentence structure: "Her head was leaned" and "in her nostrils was the odour of dusty cretonn"?
Joyce was being brave and groundbreaking here. In "Eveline" and in his famous novels he developed a whole new way of writing "au naturel" - some of his novels took this to extremes (stream of consciousness), less so in the short story "Eveline." Dublin has a lot of beautiful Edwardian houses, famous for their antique and imposing doorways and windows - although many of the ones I have seen are dilapidated and were lived in by hordes of disadvantaged people as tenements as they were abandoned by a scared and privileged upper class. This may be one such window, which is why the curtains are important as Eveline sits there for us to view, like an artists model-posed. This allows Joyce to say her head was "leaned" as if she were dead, or an inanimate statue. Certainly, the dusk invading the avenue is true - these avenues are very sweeping and gracious but were reaching the end of their era, like the country and the general atmosphere of Eveline. The "odour of cretonne" sentence is important as it is vernacular and also gives the story an atmospher of fading decadence, dust and death of country,body and soul.
This is a question of personal preference. In other words, it might sound unusual to you, but to others it is not that unusual at all, especially in structure. The first sentence is a passive construction - pretty common. In the second sentence, the prepositional phrase just comes before the predicate nominative - a little less common, but part of usual speech. If anything, I would say that the sentences were very descriptive and poetic. I like them a lot. Good luck.