Thing thing is thing is though Thalia has nothing to do with Zoes Survival rate Zoe died cause she changed to much and her pet thought she was a intruder and poisoned her before her big fight with her dad her Tallia being there doesn't change that shes changed enough to not be considered part of her family and then though it was a good idea to hide her injury. Plus instead of forcing her to join the Hunt why not just make her the child of Prophecy,
Because she doesn't want to be and we have no idea what will happen. For Percy, everything ended up fitting and we know how things turn out.
The prophecy goes
A half-blood of the eldest gods
Shall reach sixteen against all odds
And see the world in endless sleep
The hero's soul, cursed blade shall reap
A single choice shall end his days
Olympus to preserve or raze
Percy was the halfblood son of Poseidon, one of the eldest gods
Dispite all his near-death experiences, Percy made it to sixteen at the climax of the Battle of Manhattan
During the battle, every mortal was put to sleep
Luke was the hero, the cursed blade was Annabeth's knife for Luke's broken promise by the River Styx. Luke was a hero for killing Kronos who was using him as a host.
It was Percy's choice to give Luke the knife, which he used to kill himself and Kronos.
In the end Olympus was preserved because Percy chose to give Luke Annabeth's knife so that Luke could destroy Kronos by cutting his Achilles' heel (which was located under his arm).
Now, whether or not Thalia could even be the Child of Prophecy
depends on the QM and how it's decide that prophecy could go. I personally see several ways it could go.
First way is that it's Percy. The prophecy was always about Percy. Thing will twist so that Percy is the one in the prophecy. Other people who are close to fulfilling end up being killed, cursed, frozen in time, or something. For example, Thalia might end up dead after becoming human again, she might never stop being a tree, might simply die instead of becoming a tree, that sort of thing. Things will turn out that way, and each part of the prophecy will be fulfilled exactly like it was in the books.
The Second way is that whoever reaches 16 first will the the one the prophecy is about. It can be anyone. Somehow events will turn out to be fulfilled exactly like it was for Percy, just it's them instead of him. Events will end up happening years early. For example, Kronos could end up possessing Luke several years early instead of after Percy arrives, things mgiht go suddenly great for them, allowing the battle of Manhattan to happen like it did in the book, just several years before Percy turns 16.
Third, the prophecy will fit what happens even if what happens is vastly different than what happened in the book. There could be a totally new and different OC halfblood (or it could still randonly end up being Percy) and the events wont be the same as in the book, but it'll all fit in the prophecy in the end. For example, instead of every mortal in Manhattan being asleep they're all dead (thus an endless sleep), the hero is actually the same halfblood that turned 16 so they will die, or someone else other than Luke will fit the hero whose soul will be reaped (ie, the new OC halfblood or maybe Percy or Annabeth has to choose between saving Olympus at the cost of their own life at Kronos's cursed blade or letting Olympus be destroyed), the hero ends up making the wrong choice and Olympus is actually razed. All are possible and it'll fit the prophecy in the end.
There might be more ways, but those what came to mind for me. It's all up to the QM to decide how flexible the prophecy will be and what could happen.