Heh... I remember the Water Buffalo incident. I was in grad school at Penn at the time. IIRC he did not call them water buffaloes, he said "you sound like a bunch of water buffaloes." A subtle distinction to be sure, still....
My sympathies were entirely with the guy. Unlike 98+% of our population, I don't believe being a college student gives one license to disturb one's neighbors by being loud and obnoxious near where they live. So, free speech implications aside, I applauded the guy for telling the people participating in the stupid sorority initiation stunt to take a hike so he could study.
My computer's screwy and not opening the links and I'm too lazy to try to fix it now.. but from what you've posted.... the crux of the matter is her ambiguous status as a student and as an employee of Penn. Employers have every right to expect that their employees will refrain from saying things that will cause trouble for the employer. As a student, they should suck it up and ignore it. As a TA, well, maybe they should still ignore it. If it's done on her own time, and it's not reflective of her work (she did not, for example, post that the linguistics department is chock full of ignorant morons who couldn't tell a gerund from a participle) should they call her to task? I'd say the university shouldn't do anything, but her advisor if s/he is smart will warn her that she needs to consider the effect things like this will have if she plans on a career as a college professor (which I assume is the point of her being a TA). Or it's possible her advisor doesn't like her and will hang her out to dry. When you're a grad student a lot depends on your faculty.