Are you homeschooling now? Have you checked into how the GED is viewed by the admission committees of medical school? If your child graduates two years earlier than usual, will she still have all of the typical science and math credits:AP BC Calc, AP Physics C (both mechanics and E&M),AP Chemistry, AP Bio, etc.?
If you are homeschooling, there a many ways that you can challenge a gifted kid and have her graduate from high school at the typical age. The GED is viewed negatively by many. I would not recommend that route under your circumstances.