If simply explaining the policy isn't getting through to her. Use a different example.
Explain to her in some respects AOII is run like a business. We have certain requirements that we must meet in order to be considered in good standing. The chapter I belong to prides itself on (fill in the blank: strong sisterhood, outstanding philanthorpy, highest GPA among NPC groups on campus, etc.) And because of our strength in those areas, we need to make sure that our newest member already meet this criteria. We have a wonderful academic development program in our chapter and I'd really like to have you enjoy it's benefits - but first we need to make sure that your grades are above a 2.5. What can you do fall semester to get your
TOTAL ACCUM above a 2.5?
If that's the only thing denying her from membership - she's in total control of her destiny. Whether with AOII or any other group on campus.
Do you know where her grades stand? How hard will it be for her to be above 2.5. Is it an issue that she's totally wonderful and the chapter loves her and are just as disappointed that they cannot offer her a bid b/c of her grades. OR, are there other issues. You certainly don't want to lead her on and promise her a bid to any chapter. But, perhaps with this different perspective she might "get it". If not - send her to me. I'll help her!
GOOD LUCK!