But the Ballard case shows her to be inconsistent with her principle of the original life form taking precidence. Until you're familiar with that situation, you can't properly judge Janeway on this issue.
Inconsistent in what way? It was Ballard's choice to ultimately return with the Kobali, not Janeway's, and the captain accepted her right to do so, as did Kim and her fellow crewmates (even if none of them liked the idea). It's not the same as the case with Tuvix in my view, because there Janeway did make a choice for him that nobody else could make.
If Janeway respects the right's of the body's original owner, then the being that now had Ballard's body was desicating it. It still held the memories and genetic material of Ballard. The being deciding to leave Voyager was NOT Lyndsay Ballard. Her deciding to take off with the body is no different than Tuvix deciding he wanted to continue living at the expense of the lives of Tuvok and Neelix. If Janeway respects the original body owner, then she should have held the alien creature and continued attempting to restore Ballard.
If the alien inhabiting Ballard's body had the right to choose to keep the body at Lyndsay's expense, then Tuvix had the right to do the same.