Gosh Lizzie, I've looked for one for years having a child with T1 Diabetes ... and have yet to find such a recipe! I have tried reducing the sugar but with cookies you really lose the crunch and much flavour. Does it have to be sugar-free? What about mini-sized cookies using a normal cookie recipe - that way she wouldn't be consuming too much sugar?
Hope someone comes back with better advice but Happy Birthday to your LO for Saturday.