If you can fix the broken gear, that would be great. Berninas are really incredible machines, and the older models like yours are known for their excellent stitches.
Have you considered buying an adapter so that it can use generic feet? They are available at lots of places, eBay being one of them, and then you could see how the machine works before investing in specific Bernina feet. I would bet that after you try out the machine, you will want to invest in feet for her.
By the way, you can go to the Bernina website, and look up the number of the foot that came with the machine, to see what the purpose was.
Good luck--I love my Bernina.