Like the first line says, Olga was born to a noble family in Russia. What that means is her childhood home was probably a huge and gorgeous estate right in the middle of St. Petersburg. Think marble, gold, and all that other fancy stuff. The narrator describes her childhood like this: "Her childhood passed festively, securely, and gaily, as was the custom in our country since the days of old. A sunbeam falling on the cover of a Bibliothèque Rose volume at the family estate, the classical hoarfrost of the Saint Petersburg public gardens…" (2). Sounds like Olga is living the life to us. Plus, she doesn't just have an estate, but she has a summer resort too. Lucky.
But unfortunately, Olga doesn't get to stay at her estate forever. When she runs away to Berlin, she finds herself living in drastically different digs: "For about six years, that is until 1926, she resided in a boarding-house on the Augsburgerstrasse (not far from the clock)..." (6). That's a definite step down from an estate. Imagine that she went from living in all of that fanciness to something that probably looks a lot more like a dorm room. But wait, it gets worse. The narrator says: "Her father died, she moved to another street" (9). Now, that may not seem like a big deal to you, but her dad was the one who was working. So now Olga has no money at all, and she's probably living in some place way smaller than a dorm room.
Okay so she went from living in a big house to a really tiny place, so what? Have more patience! We were just about to tell you.
The Home in Russian Literature
The home is a pretty big deal in Russian literature, and most of the time "home" equaled a huge estate. You see, the way a story would go is the protagonist would grow up on this great estate. Then for some reason they leave the estate. Everything wraps up when they return to the estate, better and wiser than they were before. If they don't return to the estate, then it's assumed that the estate has been destroyed.
This is exactly what happens in Olga's story. She grows up on a wonderful estate, and is forced to leave when the revolution hits. She hopes that she can go back, but she never does, and everyone in her family dies. For at least once in the story, Nabokov totally follows the traditional status of the home in Russian literature. He just goes for the sad ending, instead of the happy one.
Memories of Old Russia
One more thing. You can't forget those émigrés, because this is their story too. That wonderful rose tinted time when Olga is a child is also their childhoods. And when Olga is nostalgic, she is expressing the same feeling that Nabokov and his contemporaries must've felt thinking about how great their lives were before they had to run away.
For them, the home is not just a traditional literary trope. For them, Olga's estate is a symbol for the estates and the childhoods that they lost as a result of the revolution.