I would say that St Louis and UBuff are the best choices, both on cost and on ranking. They offer very different experiences. St. Louis is a medium sized, Catholic school, while U Buff is a large state school. Sounds like she did not get any aid from Buffalo? Are there any merit scholarships avaiable?
I would look at cost of housing. Many students move off campus in later years and costs may go down if housing is less costly. Also, are there differences in transportation costs? Can she take a bus or get a ride home from Buffalo, but have to fly from St. Louis. Make sure to check prices during peak travel times like Thanksgiving. The $2K difference may evaporate.
I would also look at what she wants to major in and what the other options are. Many kids change majors.