Simon Powell sends in photographic proof of what I said earlier; that Sergio often has beautiful women flocking to be near him.
I don't know the young lady's name and neither did Simon but the character she's dressed as is Power Girl, a DC Comics heroine who debuted in in All Star Comics #58 (1976) by Gerry Conway, Ric Estrada and Wally Wood. I believe she was designed by Joe Orlando but her appearance was refined by Wood in her first appearances.
Fans noticed that her chest seemed to grow from issue to issue. I was around once when Woody was asked about this. He said that it was his intention to add about a half-inch to her bustline every issue and see how long it would be before someone told him to stop. Wood only did eight or nine issues and I think someone told him to stop around his sixth…but I'll bet if he'd stayed long enough on the title, he'd eventually have made up for lost time.
UPDATE: Jamie Coville sends in an identification of the lady. She's a Canadian entertainer named Liana Kerzner, better known as Liana K. Thanks, Jamie.