Dating outside the organisation is a huge no no. In the Bible the early Christians were told not to be unevenly yoked with unbelievers. In the JW world this is anyone who does not follow their faith including other christian denominations. Because this is an instruction in the Bible it is seen as a command from God so failure to follow this command is showing disloyalty to God. This person is not demonstrating the right attitude and could be marked by the congregation as someone who is not a good associate.
If they suspect you have been alone together they may decide to hold a judicial committee for fornication or brazen conduct which can result in disfellowshipping. If she repents she will be asked to cease the relationship as demonstration that she has the right attitude.
In a local congregation a witness girl started a relationship with a non believer. This person subsequently started a study and they got married. All the elders that attended the wedding were removed as elders. The feeling was even though he studied the relationship was a sign of disobedience.
In my old congregation a sister who got engaged to a non JW had a marking talk given to the whole congregation saying what a dreadful thing this was and she was to be considered a bad association.
Your relationship is under tremendous pressure JWs are not people swayed by true love everything is subordinate to loyalty to the organisation. I cannot see this ending well as the congregation will try to humiliate the girl you love to get her to conform and it is possible she will start to resent you as the perceived cause ofher pain.