When you saved the pic from her profile, what did you label it as? Maybe you had the foresight to include her name in the file name? (wacky as it sounds, this alternative thinking does have some paracticality).
If you visited her profile, you probably vivited her room, right? Maybe you tipped her. Consult your token history and you should see her name.
Maybe you didn't tip her though. But so long as you at least spoke in her room, there's still hope! Check your archives for the chat log (which will also yield this mysterious child's name).