A grade skip is a reasonable request although they may not see it as such. If you can, I'd get a copy of an Iowa Acceleration Scale and fill it in as best as you can with supporting documentation attached and either submit a letter with a formal request for a skip with the documentation and IAS attached or set up a meeting to discuss with it in hand.
Another option would be to request subject acceleration in her strongest subjects if all of the grades have reading or math at the same time for instance. Subject acceleration can be a good segue into a grade skip in later years as well.
You may have to realize that you cannot advocate for more without getting some people irritated. It is easier for the school to provide the same to everyone than it is to do something special for your child. However, there is a difference btwn advocating assertively and being accusatory or aggressive and it sounds like they aren't planning to do anything for her to accommodate her different needs at this point, which just isn't good enough.
Do you know the 3rd grade teacher she has? Would s/he be a good ally or someone who is likely to stand in your way?
