Honestly, your sister's membership probably did impact your results. I have done many recs for many women going through SEC recruitment. Those who were attending the same school where a bio sister was an active member did experience heavy cuts early on. These were outstanding young women, but going into pref, they only had their sister's chapter. Well, one of my rec girls had her sister's chapter and another one she was a legacy to.
I do know of one recent case where a PNM (attending the same SEC school as her bio sister) did pledge a different house during spring recruitment. From my years of observation as a rec-giver, this is unusual. Bio sisters at the same school do appear to usually end up in the same house. Is it because the younger sister didn't have other options? I think so in a lot of cases. A PNM I did a rec for two years ago has a younger sister who will be going through recruitment this fall. When younger sis was deciding on colleges, older sis said, "If you come to my school, just plan on being in XYZ Sorority with me." Maybe others here have seen different results and can give you more encouragement and advice.
I will say, all of the women I know facing this did pledge the same house as their bio sisters. Out of the six I know from 2011 and 2012 fall recruitment, four are completely thrilled, judging by what their mothers tell me and the pictures I see on FB! Only one was truly not happy and ended up dropping. The other one was okay with it, but once her sister graduated two semesters later, felt like she was no longer "in her sister's shadow" and could make her own place and not feel like everyone saw her as so-and-so's baby sister.
If you try again, I would caution you to expect similar results -- possibly even harsher cuts since you'll be (I assume) a sophomore.
If your sister will still be an active, hopefully you will get an opportunity there and will be open to it. Again, maybe others can share different outcomes for someone in your situation. Best wishes to you!