It’s an odd distinction to draw in any case. That Barnard is “located across the street from and part of” Columbia is simply a fact, that is both one of its positives and a possible drawback, as I pointed out in my post #2 above, in response to the OP’s query about “sense of community”.
It makes no sense to me for anyone to isolate a major asset of a university or college and use it as a negative in comparison with a different college - or to argue that another college would be more popular if only had the same quality or draw. So I agree with @exlibris97 that raising that it’s a reflection of insecurity, and, I would add, envy, to argue that somehow it diminishes the value of Barnard or its offerings. It is what it is is.
The OP hasn’t returned, but if she strongly prefers a women-only environment and the desire to be part of a close community - then she’d likely find Wellesley to be a better fit. If, on the other hand, she decides that her interest in urban life and her sense of being extremely independent are more important to her, she probably would find that the Barnard environment is more stimulating and provides more opportunities.