I am currently in my senior year in the honors program at a major research university. Not an ivy, but a very respected school. I really don't think that where I went to school made a huge impact on my lack of acceptance (i.e. I was involved with research from my freshman year, working on an honors thesis, etc.)...if you look at their website (
http://www.brynmawr.edu/postbac/facts.shtml), the majority of their students "attended large universities".
Does the fact that I was applying directly for undergrad play a role? Maybe. However, I contacted the admissions office this summer and was told that I would be at no particular disadvantage. This is all leads me to once again assume it was the SAT score.