Rachel has an odd distinction of being one of my favorite characters while simultaneously having some of my least-favorite books. The crocodile was a Rachel book, the oatmeal was a Rachel book, the Helmacrons show up in a Rachel book, the starfish book, the one with the cheetahs...
But even though the plot narratives aren't my favorite stories, I do think it's important to note that Rachel is very, even early on in the series, acutely aware of the direction the war is taking her. She doesn't start out as Xena, necessarily, but she starts off as the girl that, push comes to shove, will not only shove, but shove hard enough that no one else needs to shove. Rachel, as elephant or grizzly, absorbs bullets. There is something of a "shoot me; I can take it" strategy to how Rachel is used in battle. Not that she doesn't also do a ton of offensive lifting, but that doing the heavy hitting up the middle makes her both a goddamn hammer and a huge fucking target.
But it starts as "I can do this so you don't have to" and it evolves slowly over the series.
"I did this before, so I can do it again..."
But also, Rachel is the oldest child in a family with divorced parents. Her relationship with her parents is explored in a few instances. Her dad asking her to live with him in #12. Naomi not being able to adapt to not being in charge at the end of the series actually forever retroactively colored my view of her as something of a control freak. Her relationship with her sister honestly could have gotten more screen time.
But Rachel as juggernaut was an identity she could control. She didn't have a say in her homelife. Didn't have a say in the divorce. Had to give up living with her dad to stay an Animorph. All the things around her that she juggled. Gymnastics is a sport that is 100% about precision. She got an award for scholastic achievement. Rachel, prior to being an Animorph, was a girl that went where she was told, did what she was told, and tried as hard as she could to excel, to succeed, etc. I actually as an adult picked up on the idea that Rachel's obsession with fashion was less teen-magazine 90s stuff and more her deciding who she was in one of the only avenues her parents let her have. She can't control this or that, but damn it, she can control what she's wearing, how she looks, etc. I do still think Rachel wearing expensive designer fashions does say something about her mom maybe making sure her kids "look the part" or something, but I definitely see clothes as an area where Rachel is given a lot of freedom and she sure as hell exercises the hell out of it.
But anyway, "I can do this" starts to devolve.
The team dynamic inevitably turns "she can do this" into a foundational pillar. They lean on her so much that they stop checking in on her.
Push comes to shove becomes shove first so they don't have time to push at all. She manifests an aggressive personality she didn't used to have. By the time she realizes how traumatized she was from the first few missions, they're halfway through the series and she doesn't know how to cope with it.
Rachel never asks for help.
I'm not sure if that was a pride thing. If she pathologically couldn't get to a place where she could honestly admit to herself how not okay she was to have to ask for help. Or if she felt asking for help was an admission if failure. Or if she thought asking for help would put somebody else in her seat, make someone else be the pillar. I think knowing what her role in the team was to that point, she definitely had a severe guilt complex about asking anyone else to help her carry that burden.
But even more fucked up is that literally every single member of her team saw her breaking, saw the cracks in that pillar, and didn't ask to help. Jake repeatedly made her wear that crown. He made her wear it knowing it would kill her. Made her wear it till neither of them knew who she was without it. But Jake was the general, the leader. The shot caller has to know what tools he has and to a point, Jake had to use what he had.
But Tobias knew what she was becoming and didn't lean on her. He lost every last proton of his humanity at some point or another in the series. He knew what it's like to lose oneself and he didn't offer to listen, to help her transition from past Rachel to new Rachel. If anyone on the team knew fundamentally what it's like to become a predator, a killer through and through, it was Tobias. And he didn't help her.
Marco was the strategic genius. The ruthless one. He saw what was happening to Rachel. Hell, I think he was the first one to notice that she crossed a line from being good in a fight to needing a fight to define who she was. He was the one to name her Xena. A joke at first, then ultimately a brand.
But Cassie was the heart of the team. Their conscience. She was their moral compass in most ways. But Cassie also had a judgmental side. She didn't agree with the way Rachel went about the war, and I think the wedge that grows through their relationship was important but a little too off-page. They slowly go from best friends at the beginning to almost strangers by the end. But Cassie knew Rachel wasn't okay, and because she didn't help.
All four of them, in some way or another, knew the war was killing Rachel. And at some point, all four of them decided it was okay... right up until she died. And then and only then, did they realize what they did to her.