Question:
Ben, I just came across an old textile manual on stain removal. It says that for perspiration stains, to soak the garment in a 10% acetic acid solution. You could use white vinegar instead, which contains acetic acid, although I think most vinegar sold in the supermarket has about 5% acidity. You could find a vinegar with a higher 10% acidity in a restaurant supply store. But perhaps you have some acetic acid in the machine shop?
But I'm sure that just soaking it in plain white supermarket vinegar for a few hours (and rubbing some into the really stinky parts of the shirt), would do the trick. Then just wash it out. And then wash it out again so you don't smell like a salad.

Answer:
Are you sure it was your GF and not you? I noticed that several of my t-shirts smell a little in the armpit area, so I just put some tide specifically on the armpits on those select t-shirts before I put in the standard amount of tide in my load. I have found this works.

Answer:
They make many enzyme products to help get rid of "organic" smells caused by pets.
I've used products called "Odor Mute" and "Simple Solution" and they have worked great on removing all sorts of smells. They are really gentle and may work on human smells as well!

Answer:
Maybe you could make a paste of baking soda or wet but unused kitty litter and let it sit for awhile before washing. I don't know what color it is, but I'd test for color removal first.