Tuvix is literally just a Trolley Problem scenario with a fancy costume. No more, no less. And the whole point of the trolley problem is that there isn’t any single “correct” answer.
There is an out of control trolley. You can’t stop it. On the trolley’s current track, there are two people. If you do nothing, they will die when the trolley hits them. But you’re at a track switch, and can divert the trolley to an alternate track. On that second track, there is one person who will die if the trolley hits them. Do you pull the lever? If you pull the lever, are you murdering the one? If you don’t pull the lever, are you complicit in the deaths of the two?
In this case, the trolley is the transporter accident; Janeway has the ability to pull the lever and reverse the accident. If she chooses not to, she is essentially refusing to pull the lever, thereby condemning the two people on the first track to die. But if she reverses the accident, she is pulling the lever and killing the one.
Janeway decided the answer to “should you pull the lever” was “yes”. She pulled the lever, saved the two, and killed the one. Sure, you could argue that pulling the lever is murdering the one. But if you sit by and do nothing, aren’t you willfully (maybe even maliciously) negligent? After all, you have the opportunity to save the lives of two, while minimizing damage to only one person.
Philosophers will try to change the trolley problem to fit different scenarios. What if it’s a bunch of convicted felons on the first track, and an innocent child on the second track? What if it’s a bunch of your friends and family on the first track, and your worst enemy on the second? What if, what if, what if… But the base question is always the same; Do you choose to do nothing and let many die, or actively kill the one? What is the tipping point where your decision changes?