Sarah,
I am not an expert in rush, but here are some things to consider.
1. Get those graduates to come back and help with rush. (Hopefully your campus doesn't have rules against alumnae helping with rush!). This would be vital for you guys. They still know the campus, your sisters, etc. and would be the best fit. Of course, any alumnae to help you with rush would be great!
2. Does your chapter have a positive reputation on campus? Be honest about why you lost half of your chapter! Graduation is a great thing, that's why all of you are there!! Project an air of pride and confidence about this situation. Brag on those girls and the wonderful careers they now (hopefully!) have. See if a few of them will commit to visiting the chapter to talk about "life after college" and see if that would be a selling point also.
3. Is your chapter going to convention? If so, go find Susan Watson Hardy (National Recruitment Coordinator), or Elaine Martin-Kneebone (Parliamentarian, but the best dang rusher I have ever seen!!) and ask them for help. Of course, convention is where you can ask all of the chapters for help, and see which ones can come to you for rush.
I don't have any really good ideas for philanthropy party, but one thing that I would be impressed with (as a rushee) is doing something that can be continued when I join (like painting flowerpots that we can later put a plant in and take to a nursing home as a NM class--ok, kinda cheezy idea, but it was easy to explain!!
) This would help me see myself on the other side. . .what would I be doing once I pledged?
BTW. . . you are not the first chapter to have this dilemma, and I have seen chapters turn this around easily. This is where rush 24/7/365 really comes into play. Prepare to COB like crazy!!!
I hope I could help!!! Are you going to convention?
Tau Love,
Teena