Agree that's good way of making it plausible that she acquired some that way, although I imagine #4 is probably hard to do because the actual animal itself is long consumed. The best you can show is that it's fairly likely what you ate would contain the banned substance.
Perhaps it's enough doubt to get you off, but even if Houlihan could do #4 or #5, it still doesn't establish that she didn't cheat. She could have been doping with nandrolone *and* ingested nandrolone from the burrito.
I guess I'm open to the argument that *proving* you got nandrolone from a pig would create a sufficient enough amount of doubt (e.g. odds of being on nandrolone AND by chance also getting a big dose are not that high unless planned) for exoneration.
Unfortunately, that sets up a conveniently useful precedent for how to get away with doping in the future: Find animal with desired banned substance routinely found in it's body -> dope away -> eat the animal regularly -> if test positive then "Oh but it was the animal I ate"