I think there is too much smoke, from too many places, not to have at least a little bit of a fire here. She was not an "outcast" as far as Troy and Greg are concerned, yet Troy doesn't like her and Greg singled her out as the one person he wouldn't be friends with IRL. Someone in a secret scene mentioned that she talks nonstop and it's irritating.
As for why Christina has been outcast, I think the main reason is she wasn't part of Alicia's instant 5 alliance on Day One. People being people, they tend to find reasons for why the excluded person deserves to be excluded even if the same behavior by an insider wouldn't be criticized. Outsiders are sneaky, insiders are strategic; outsiders are crazy, insiders are eccentric; outsiders are meek or passive, insiders are thoughtful and patient.
Greg/Tarzan has had problems with pretty much everyone, except perhaps Kim. That Tarzan has had problems with Christina is no evidence, IMO, that there's fire.
Troy/Troyzan never thought of Christina as an ally since Christina was part of nuManano and Troyzan thought he was part of a nuSalani alliance. Moreover, Troy/Troyzan & Christina have been competing for next boot and that's bound to cause some friction.
As for Christina's alleged non-stop talking, that doesn't contradict my point, that when an outsider and insider engage in the same behavior, the outsider is scorned and the insider is praised or tolerated. Moreover, since Christina is an outsider, the insiders may have a much lower tolerance for her talking than they would an insider (shades of Chelsea telling Troyzan to take it like a man, i.e. to shut-up). And this being Survivor, sooner or later everyone gets irritated with everyone else at some point.
That's an interesting hypothesis, Constantinople, and it may have some merit (though I wonder why the contempt seemed to extend to the feelings of the men as well).
All of the men thought they were either part of the nuSalani alliance, to which Christina was an outsider, or were part of the existing majority alliance on oldManano that carried over to nuManano, to which Christina was also an outsider.
As for racism, Alicia of the slitty eye gestures put together the original women's alliance on Day 1, so I think it's fair to attribute Christina's outsider status, at least in part, to racism. This doesn't mean that anyone else is racist, just that, once Christina became an outsider, the momentum of tribal dynamics kept pushing her away.