A Gryffindor with dark eyes and long, dark hair, Romilda made it very obvious in her fourth year that she was pursuing Harry Potter (HBP7). Among other things she tried out for the Gryffindor Quidditch team (HBP11) and put a strong love potion in Chocolate Cauldrons she gave Harry, which had inadvertently disastrous results when Ron ate them by mistake and fell madly in love with her (HBP18). Even when Harry began dating Ginny, Romilda’s interest did not wane; she inquired of Ginny whether or not Harry has a hippogriff tattoo on his chest (HBP25).
"Vane" is a play on "vain," meaning excessively prideful.
Romilda is one of three known characters who entered Hogwarts in 1993 (along with Astoria Greengrass and Derek, who has a cameo in PA11). That grade had a rather unenviable time at Hogwarts: their very first year saw dementors at Hogwarts as Sirius Black tried to break in, and instead of taking their O.W.L.s (which determine their entire future), they had the Battle of Hogwarts.