If your girlfriend doesnt get why we love to build bows instead of just buying a nice new shiny factory bow, have her spend some time here, look at the caliber of the work of people like Pat B, Manny, Orcbow, Gordon, Frank, Bernie, and the rest. She may start to understand the allure of building wooden bows then, and why we love to make things with our hands, the satisfaction of hunting or target shooting with your own gear, etc.
You dont have to spend a lot too. Just a few basic hand tools (farriers rasp, wood rasp, files, hand saw, small hatchet, cabinet scraper can be all you will need), and invest in a red oak board from Lowes or Home Deport, and get to work. Get some advice here about selecting the right kind of board, so the grain configuration is right to get a successful bow, and making a sting is an easy thing. Some scrap leather from a thrift store or leather store for a handle, and you have a one of a kind hunting bow you made yourself.
The best advice is to go slow, take your time, learn from what you do wrong, and enjoy yourself. Nothing better than spending some time in the shop by youself creating a deadly thing of beauty.
Dane