1. Reapply and risk rejection. A second rejection will affect future visitor visa applications, but will not make a difference if you get married and then sponsor her.
2. Do not reapply
That's about it. Not sure what you're looking for.
There is ordering the case notes from the TRV application. Ideally you'll get a more detailed explanation why she was rejected, but there's also a change you'll get vague and generic reasons, depending on the officer's mood.