I go to NU too and if I were you I would totally rush again! So many sophomores go through every year and almost all of those who participate all the way during rush and then fill up their bid card completely do get bids - and basically every house will take a few sophomores! As SororityGirlNWU suggested, you may be asked some questions about why you depledged last year - but it sounds like it wasn't your fault. Anyway, good luck convincing your mom to let you join a sorority! Also, I have heard that the greek scene at NU has changed so much over the years - thirty or so years ago, we had chapters of a bunch of sororities we dont have now, like Alpha Gamma Delta, Alpha Omicron Pi, and Phi Mu. So who knows what your mom's chapter is like now?

Good luck to you!