Best way to go about starting a mean 3yr old?

You have to get her curious about you, go into her pen for a while and don't touch her or go near her, just stand or sit with your head turned away from her, it might take a while, a few times of doing that for as long as you can, and I can't grantee it will work, but it is worth a shot and I have had some success with it, another thing you could try is Join-Up, there are some good examples on YouTube you can look at for how to do it. Whenever my horse gets a bad attitude I work him in my round pen for a bit, turning him often and making him really work, he knows if he accepts my challenge for leadership he gets to stop working, but he has to be calm, and accepting, otherwise he gets to work more. I wouldn't give up on her to easily though, you just got her and it may take some time for her to relax and accept you, but if it starts turning into more than a few months of working her, getting a trainer would be a good idea, but keep at it, and you should get some results.