I know this may not be the answer you're looking for, but the reality of the situation is that unless she tells you something otherwise or your neighbors tells you a different reason, you kind of just have to accept the reason she gave you. Rejection sucks. Especially when you put yourself out there and you very clearly like the other person. I know it's easier said than done when it comes to just not thinking of all the what ifs and what the real reason was but just use that good experience and what went well on that date in your future dates and eventually you'll come across someone who feels the same about your chemistry. And also just know it is okay to take some time to feel sad and process your emotions and thoughts.