Not even Federation law would be in effect for Janeway's actions on Voyager, because I'm sure there would be a UCMJ (Uniform Code of Military Justice) for people serving in Starfleet. What happened to Lessing will probably be considered a good cop, bad cop tactic by anyone who looks at it objectively. After all, only Janeway knows whether she would have let the beasties kill Lessing; Chakotay only knows that he backed down first. I'm sure the captains in other series did things just as reprehensible. I remember an episode of ENT where Archer nearly killed a man being held prisoner.
And let's put the Equinox bunch in a strong light. Not only were they premeditated murderers of a sentient race (and for their own benefit), they left Voyager and her crew as vulnerable as Equinox had been when Voyager rescued them. Instead of joining Voyager's crew, they took the new shielding that the Voyager crew had helped them design and left their rescuers to the wolves. They had to hope that Voyager and her crew were killed because otherwise they would report on their crimes (eventually) and find themselves on trial for treason. In light of that, I think Janeway's passion and antagonism are not just understandable, but justifiable.
The Equinox Janeway is always the one latched upon by those who haven't seen much of Voyager as proof of
Janeway's "insanity." In fact, it was one act in thousands over a period of seven years, and one that has to be the worst possible situation for a captain charged with protecting the lives of her crew and the existence of her ship. The Year of Hell Janeway is just as valid an example of her character, as is "The Void" Janeway from the seventh season where she creates a "mini-Federation" and escapes from their predicament. That isn't to say that her character was consistently "perfect," but much of that happened when TPTB were so busy creating the "better" Enterprise. What a laugh.
Finally, Janeway was a captain under duress from the first. To expect her to be the model of propriety in her situation is expecting too much, IMHO. She does pretty well when you take her situation into account.
YMMV