Here's the thing: the members of the chapters on your campus probably won't bring up your grades during round one because way too many girls will be rushing for them to remember your GPA and make that connection when they see you. I'm assuming you won't bring it up because you won't want to draw negative attention to yourself (regardless of your excuse, if you bring it up you'll be known as the girl with the low GPA who has an excuse for everything). When grade cuts are made, they are made because the chapter has academic standards they hold themselves to... your excuse won't matter when a chapter plans to cut everyone with a GPA below a 3.0 or a 2.8 or whatever. I would assume that in an SEC rush you will be cut by most houses very early on if you have a 2.5 high school GPA. Sherbertlemons makes a great comment about GPAs typically dropping... who wants a girl who might be on academic probation spring semester?
I'm surprised that you're attending an SEC school that doesn't post a minimum GPA for recruitment... how else would PNMs know whether or not to bother signing up? I think Auburn addresses the question of how much high school GPA will matter particularly well:
https://fp.auburn.edu/greek/grades.htm