First, she mentioned PyCon in that Twitter conversation. If she had hashtagged it, there would be a stronger argument, but either way we might say she's having an "inappropriate conversation" in the "vicinity" of the conference. People searching about conference might see this, just like people at the conference might have heard the same inappropriate joke.
If we look deeper I think "but she made similar jokes" has other merit. What's the point of having "professionalism" rules at a conference? Because everyone is there publicly representing a company, and because they don't want distractions from the purposes of the conference.
Adria is a public representative of her company, and apparently uses her Twitter account in connection with that. Why does she get to mix her personal life into a public-facing account, complete with "overhearable" unprofessional jokes, but two friends in the same room with her can't do the same?
The only good reason I can think of is "because the conference rules say so, and they all agreed to them." Any other reason for her getting to be offended about a joke quietly exchanged between two well-acquainted professionals but overhearable in public, is hypocritical, because she set up the exact same situation on Twitter. When you consider her inappropriate, overreacting, passive-aggressive response, and calling them "ass clowns" on her blog (it's at least partially profesionally-oriented, by the way), it just gets more frustrating.