She DID calm down after a couple of hours with the e collar on. It's still not her favourite thing ever and she sometimes flomps over and tries to kick it off after trying to groom herself and not being able to... but she's not doing anything that makes me think she could hurt herself anymore.
Also.... I swear, the basic care articles and printouts you get from the internet and vets should all come with a standard clause involving "By the way, this may be a lot more difficult than it sounds. Here's some basic reasons why. And here's some common ways to deal with those things."
Somehow, I have never seen anything or spoken to anyone that gave that kind of warning. You read and research and post and it sounds like spaying and neutering are just simple, formulaic chores to be handled with these few easy steps. No one ever seems to mention "Oh, and also, your cat may go completely psychotic in reaction to a cone of shame and may require many, many hours of constant hands-on attention in order to determine how to best keep her safe and comfortable and keep her from hurting herself."
I feel like there are going to be people glaring at me all like "Well isn't that common sense??" but... well... no. It's not. Some animals, if they need something done, you just poke them with an injection or knock them out and cut something off or hide pills in their food for a certain amount of time and after that, they're good to go. All the cats we've ever owned had been fixed before we adopted them, and remained in good enough health for the rest of their natural lives that we never had to deal with anything more complicated than routine checkups with them. So... I guess it is a logical progression to figure out that a mammal who has just had a couple of major organs surgically removed is going to be challenging to care for until she heals, but the logical progression still doesn't give you any way to guess HOW challenging.