see the bit that would worry me is the fact she is your girlfriend, is she for forever and if so why is she not your wife,(none of my business)
Can you imagine a split up a few years down the line and the claims of I helped build the business etc, and in this case she could prove she indeed help.
If she really wants to be part of the business get her on the tools for six months so she understands what the lads are doing, preferably through the winter