Do you care about your girlfriend?
Do you agree that it is *possible *that having a front and rear brake might be safer?
Do you agree that there is no disadvantage in having two brakes?
If it's yes, yes and yes then just fit the bloody back brake.
And also, why not show her the arguments here and let her make her own mind up, it being her bike and her safety that is at issue?
Do you care about your girlfriend?
Do you agree that it is *possible *that having a front and rear brake might be safer?
Do you agree that there is no disadvantage in having two brakes?
If it's yes, yes and yes then just fit the bloody back brake.
And also, why not show her the arguments here and let her make her own mind up, it being her bike and her safety that is at issue?