Alternately Alternately: This conflict is not a simple "vs. The Empire" fight, despite the fact that The Empire is fighting, but is very morally gray. The truth is, Eva is the most black and white character there, but the shifting ideals, policies, and harm each is doing causes the person who benefits from Eva's help, and who's help benefits Eva, to constantly change, but Eva herself never really changes "sides". This makes it seem as if she is constantly betraying both sides.
Inverted: Eva is a loyal agent, but her agency keeps going over to the side of good... then evil... then good again.
After joining the heroes, Eva appears to betray them... but is actually just pretending to rejoin The Empire so she can snag the MacGuffin.
Eva sometimes fights alongside the heroes and sometimes against them, but eventually reveals that when she fights against them, it's only to make them stronger.
Actually, she did join the empire, but did so carefully so that she could claim to be only after the MacGuffin if it looked like the heroes would win, which they did.
Eva's story doesn't actually check out. Many of the fights had far too much at stake, and no useful lesson. The whole Trickster Mentor thing is just another mask.
Parodied: Eva just so happens to switch sides right before she gets her reward for following that side, and keeps making the same mistake every time she switches.
Discussed: "I still can't trust Eva. I just can't, there's no reason to. She doesn't even seem as though she's changed at all since she stabbed us in the back already, what's to say she won't do it again when things get tough?"
Conversed: "I've lost track: which side is Eva on this episode?"
Deconstructed: The Empire has been helping Eva achieve her dreams, but she starts questioning their methods after meeting Alice and Bob and ends up joining their fight. However, her past makes it difficult for her to fit in with the other heroes, and she goes back to The Empire... but can't stand working for them knowing all they've done, so she rejoins the heroes. But now they trust her even less, and she doesn't have anywhere she fits in anymore.
Or so she thinks. While Alice and Bob are still unwilling to trust her, Wide-Eyed Idealist Colin has been going to bat for Eva every time the discussion turns in that direction and has been very convincing in his defense, finally making Alice and Bob agree to give her at least one more chance. Accepted into the group once more, Eva finds a place she can do good and comes to settle in.