The spell can work without winning the fight
During The Price, Diana tries several different responses to the energy creature. In #13 she says dissolve while casting against the energy wrapped around her head. The restraint bursts apart, but the creature itself is still there. Later she uses a spell to extinguish the lighthouse fire in Uruguay, with a large water-like fall sweeping over the structure. That helps the people at the scene. It doesn't solve the creature. A later montage shows another orange-red magical attack in Merida, again without ending the threat.
The clearest example is the little orange vial in #14. She tells the creature to sleep and throws the magic at it. It reacts and temporarily withdraws. Diana notes that magic affects it more than brute force, but even that is barely a weakness. She isn't sure sleep is the right word for what happened. So this belongs in the inventory as a sleep-intended vial attack with a temporary effect, not a guaranteed knockout potion.
There is also the effect the creature has on her. Being near it amplifies her anger and darker thoughts, and she keeps having to notice and resist that change. That is the creature's hostile influence, not Diana acquiring a rage power.
Calling a goddess has conditions
Diana doesn't beat the energy creature by finding an even bigger projectile. She eventually takes the problem to Gaia. First she realizes the creature is tied to her, then she and her friends question the assumption that her existence is the imbalance that needs correcting. That distinction is the whole reason the eventual solution works. It isn't a universal rule that doing good creates an equally powerful evil double. Gaia ultimately recognizes that the world itself is already wrong.
The approach to Gaia is not casual. Diana says reaching a god will be easier from a sacred site. In Samothrace she lets the fight draw her blood, then offers that blood and pain to Demeter and asks for an audience with Gaia. She is asking one goddess to grant passage to another. When she arrives, the living earth surrounds and binds her. Trying to cut her way through doesn't work as an approach to the goddess. She has to stop, submit and ask to be heard.
Gaia agrees that something is wrong, requires Diana's commitment to fight that darkness in her name, and destroys the creature. The earth takes it apart. Diana watches rather than casting the finishing spell herself. That belongs under a divine audience, offering and bargain, not a repeatable Gaia attack she can now fire whenever she likes.
An earlier prayer works on a smaller scale. After Io disappears in the lightning at the Hieron's threshold, Diana asks Hecate for a sign that Io lives. A white bird brings a branch, and Diana thanks her. The next scenes show Io alive with Hippolyta on Themyscira. It is a response to a prayer, not proof Diana has an automatic spell that locates any missing person.
The spell can work without winning the fight
· Absolute Wonder Woman Magic