Good things may come out of this. I'm guessing, that as you've posted here, you know that having a girlfriend is wrong but that u'd like to make it halaal if poss.
best think u can do as the brother advised before is to invite her to Islam. why dont u tel her about Islam or give her some stuff to read/websites...invite her here

has she expressed any interest in Islam at all...does she ask about ur religion/culture.
I reverted because of a Muslim guy who invted me to Islam. I was never extremely friendly with him but alhamdululillah he initiated my acceptance of Islam. To this day we do not keep in touch but I am always grateful to him for bringing me to Islam.
Also, you need to stop any haramness.....girlfriendy/boyfriendy type activity inshAllah it will be in ur best interests too.
May Allah guide you and reward you for all that you do good inshAllah....ameen