Garbage mask in Premiere or if you have access to AE and Mocha you can track a mask pretty easily.
I ended up duplicating the layer and used the garbage mask to take out everything except the green on her shirt and set up keyframes to adjust for her movement. That worked but not sure if that is the proper method. Is there a way to mask the ultrakey on the same layer? I am not experienced using masks.
It sounds like you did it the right way. Or, rather, the easiest, most common way.
It is possible to take the video, mess with the levels until you get all black or white, and use that as a mask. If you reduce the mask a bit you can avoid messing up any edges.
The advantage of that is that you don't have to keyframe. But that only works with some video. If there are soft edges like hair it won't work very well. But for clothing it is usually OK. Sometimes the movement is so radical that creating a mask out of the video itself can be a real time saver.