"That’s a lot more effective than 'go vegan.'"
That depends on what one means by "effective;" if it means to effect change, I'm not so sure. Surely Jill has considered the great difficulty of effecting even one of Niman's proposals. There are powerful economic interests, structural impediments, and cultural norms that entrench the status quo and make these changes difficult. It requires strengthening a political movement to elect the representatives willing to make such changes, and then the political pressure to make them do so. It takes cultural work of building the political will to make it possible (or necessary) for politicians to take on those entrenched, self-interested opponents, and to change people's attitude that being able to eat lots of cheap meat is a priority over concern for animals.
On the other hand, going vegan simply requires you to stop consuming animal products. As a movement, it also means convincing others to stop consuming animal products.
It's possible the political reform movement can effect change greater than the attempt to convince people to change their personal behavior (obviously people's personal behavior is quite entrenched as well, as you can see by the lengths people go to defend eating animals), but I'm not sure.
Jill's argument also raised a theoretical question: why is an animal worthy of enough moral concern that it should be treated nicely before being killed for your pleasure, but not worthy of enough moral concern to not be killed for your pleasure at all? The position that animals should be treated nicely before being killed assumes that an animal's suffering matters--yet it still assumes that the meat eater's pleasure is more important than that animal's suffering. That's not terribly much moral concern, however much better it makes a meat eater feel.