First, a note. The English title of this story is "A Russian Beauty," but the Russian title is a little different. It's just "A Beauty" ("Krasavitsa" in Russian). Since this is what Nabokov originally intended to title the story, we'll go with that.
"A Beauty" is a pretty generic title, isn't it? It's not even a sleeping beauty, or the most beautiful woman of all. It's just a beauty. But we think this is the idea: the title is meant to be generic. Olga has a generic Russian name, she seems like a generic Russian girl, and she shares a generic Russian émigré story. She's not special, and we don't really know a lot of details about her besides that she's pretty.
So the title is perfect. A simple generic title, for a (seemingly) simple generic story, about a beautiful generic girl. Or, at least until you dig a little deeper.