Wow that is really tough. I agree to get her evaluated asap...she could have some sensory issues. In my experience, pediatricians don't know much about sensory issues at all. Talk to your friends, your ped, even a local nursery school to find an OT/ST that specializes in oral motor and sensory issues.
Have you noticed that she prefers to eat dry and crunchy things as opposed to soft and mushy? Try to see a pattern.
I have a nephew who has oral motor/sensory issues, and I know how much his Mom struggled and tried to get him help, it really is hard and you have to be a noisy, noisy Mom!!! My nephew, he simply *can't* eat anything that isn't crunchy/dry/hard. He just can't do it, it isn't behavioural at all, he would rather starve.
And if I may...please don't be offended, but I would steer clear of forcing. It will only make matters worse, and may cause her to lose trust in you. While you search for help, look for any simlarity in the things she will eat....and them make those things the best they can be for her. i.e., if she likes cake, make her healthy, hearty muffins. If she likes waffles, only offer the whole-grain kind with lots of fiber.
I know it's so hard.....she needs a bit of help.