I'm pretty sure if a girl says you're astrologically incompatible that is likely to become a self-fulfilling prophecy, if nothing else. It also might suggest that she is looking for confirmations about how she already feels, i.e., that you're incompatible. That's pretty obvious, but I just thought I'd go ahead and say it.
This question comes to mind: what comes first the chicken or the egg? Self fulfilling prophecy often plays out in the map of the stars and ability to effectively and positively deal with challenging people and situations also can play out in a diagram of the heavens. She will probably find confirmation if she is determined that something will not work out. On the contrary an open heart and mind also has its confirmation in physical and astrological phenomena. So you see the hand of destiny plays out it's cards either way. If we so choose we may use difficult aspects and their energy to transform our challenges into victories. But almost all people with few exceptions remain pawns to the events of the heavens hardly looking towards the transformation of energies that have the capability and potential of manifesting in different ways because of the impetus of those intense energy interplays.
Difficult solar patterns between charts is shown by tight squares and opposition's to ones partners solar energies.
There can be mitigating features from other planetary influences which could help bring understanding to work out these forces.