colds are not the cause of cold sores. cold sores are caused by the herpes virus and yes they can be transmitted if your girlfriend has an active herpes lesion on your lip and you have never had them before. if you yourself had cold sores in the past you already have the herpes viruses in your system so it is unlikely that a new exposure would reactive it.
i kissed my girlfriend when she had a cold for about 1 week and a half i have never had a cold sore will iget them now. have i contracted herpes even though i haven't had symptoms for about 6 months