When Dorian Gray is at the opium den, a woman approaches and calls him "Prince Charming", prompting the pursuit and then confrontation with James Vane.
After being deceived into letting Dorian escape, James talks to that woman again, who reveals Dorian's ageless spell and claims "it's been nigh eighteen years" since he made her become... whatever she was at the moment (an addict?).
Now, in order for her to know his old nickname, she had to be around Sybil Vane somehow. At the same time, having been around him long enough to learn about his eternal youth (and the rumors about his dealings with the devil), she should have been able to identify him by name. Yet, she doesn't tell it to James in their brief encounter, even though she wanted him to pay for her stay at the den (and he refused) and could have leveraged that information.
I can't think of any female character that could fill in her shoes. James' mother surely would be able to identify him, but he wouldn't second-guess her. It was to be expected she would have told him about the ageless spell.
Who is her? How does she remember his face so vividly after 18 years but be unaware of his name? What's her connection to Sybil Vane? And what did he do to "make her" what she had become?