She enjoyed the adrenaline rush and the sense of purpose, NOT the combat. I'm barely restraining myself from saying "DUH!" here.
Almost every single one of the Katherine-written books deals with that balance. The ghostwriters turned her into a gymnastic shopping Punisher, but that was limited between the books in the late 20's-40's. That's not Rachel. That's ghostwriters not paying enough attention to the character they were being paid to write.
Rachel could live without the war. She'd just have to take up bungee jumping or extreme snowboarding or something as a hobby.
The entire thing with Rachel is that she was a smart, moral, strong-willed kid who was about the one and only person who didn't give a crap about her looks, she didn't even care. She was pigeonholed into that tall blonde ditzy mallcrawler stereotype, and loved the idea that the Animorphs gave her a chance to reach her potential, to live an IMPORTANT life where she could use that inner strength in the same way Jake could.
There's much more of a nuance there than "Rachel liked beating people up, so she'd go crazy without the war." That's really really ignorant of basically every single one of the Rachel-narrated Katherine books.