I started this series when I was seven. Now, at twenty-three, I have just finally finished the final book. It was heartbreaking reading about Rachel's death, and the collapsed relationship of Cassie, Jake, and the other Animorphs.
Rachel's death seemed strange and unnecessary, ultimately serving as not much more than a reminder about the devastation of war.
By the end of the series, Rachel had turned into a beast. She scared pretty much everybody around her, even her family, and would probably never be the same. I think Rachel should have won her fight. She should have gone on to slay Tom and the other controllermorphs on the ship. She should have lost a limb, an eye, gone down bleeding and scarred and cut open and passed out. But she should have survived as a nothlit, a permanent bear.
It would be tragic to see her as this monstrous creature, covered in scars, hobbling along and no longer able to fight properly. Cassie and her parents would have had to stitch her up and push her guts back in. The beautiful girl forever transformed into a disfigured grizzly bear, which by the end, probably better represented Rachel for what she was and had become.
Then, later, after a few years or so, Jake hears from Tobias. Rachel isn't doing too well. The Animorphs get back together and spend their last few moments with Rachel, who, tough as ever, then eventually lays her big head down on the ground to sleep forever. That's the ending she deserved.