To the OP:
Being from Illinois, I feel for all the chapters (fraternity or sorority) after the shootings. Now is the time to call your alumnae so that they can help. This is the time for your alumnae to become really active so that the undergraduate chapters can continue to function. Tell your alumnae that you need their help- now. You still have 2/3 of the summer to arrange for a successful rush.
After reading your post, I'd be calling my national's NIU chapter president with an offer to help in any way that I could, but my national does not have a chapter there. I can appreciate your concern-make sure that you express it to your alumnae. If you don't have a "Slightly Older Sister" program or something like it, it would help to implement it. This is when alumnae relations become important. Let us know how it goes.