But you can't determine that she's a pedophile because she roleplays having virtual child-esque sex with other consenting adults.
Your argument is that the roleplaying makes more acceptable for them the longer they do it. By that logic there would be rash outbreaks of adults murdering one another uncontrollably between desensitizing violent movies, news, music and video games.
By the time you're an adult, which is what people who roleplay ageplay are, your mental state is pretty firmly locked down. You're not going to do behavior in RL that you roleplay in a video game unless you were already going to do it anyway. What it comes down to it is it's consenting adults roleplaying something that most of us, for good reasons to be sure some of the time, are uncomfortable with. But that doesn't make it reasonable to freak out over it. I have a lot of problems understanding Gor, or BDSM, or a long list of varying other
SL social cliques that I nevertheless rarely give a fuck about until it's in my face.
There's no correlation between pedophilia and ageplay. It's convenient logic to ostracize consenting adults doing something we don't like, and I have a problem with that however I feel about ageplay in general.