If she holds a UK passport she can come over on a visit visa (she would need to fly out every other month) but she could stay with you until you are married and able to sponsor her. Obviously it isn't legal, but it isn't like they are going to come knock on your door and ask to see your license.

The only problem is with her working. If she gets sponsored by another company they may have issues with her living with you (depends on the personal beliefs of the sponsor).