If it were an LGBT group, and almost everyone in it were straight, or a women's group populated almost entirely by men, that would defeat the purpose of having a space specifically for a minority group. The same principle applies here--if you've got a multicultural group overwhelmed entirely by the majority culture, it's not really multicultural anymore.
It's a valid concern. It just needs to be expressed in a constructive manner, and it wasn't.
Her exact statement is:
"If ya'll didn't know, this is MSC and frankly there are just too many white people in here and this is a space for people of color. So just be really cognizant of the space that you're taking up because it does make some of us POC uncomfortable when we see too many white people in here. It's only been opened for four days, and frankly there's the whole university for a lot of y'all to be at, and there’s very few spaces for us, so keep that in mind."
I think she'd have been better off writing a piece for the student newspaper, since that's really a more appropriate vehicle for bringing up something like this, but compared to some of what I've seen in racial studies circles, this is really very tame.
The university has made a statement saying that all are welcome, so it's certainly not endorsing her message. Maybe someone needs to have a conversation with her on cultural sensitivity, but I don't really see a need for punishment.