@autumn_413287 For the missing worlds, please try repairing your game in Origin: open your game library, right-click on the Sims 4 icon, and select Repair. If you can't repair, start by clearing Origin's cache, then restart your computer, and try to repair again.
https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/
This may also help with at least some of the other issues, so please have a look around in-game, and let me know what is and isn't fixed.
It's possible that some of your mods and cc items aren't compatible with the Cats & Dogs EP, or rather that they're broken or corrupt in a way that wouldn't be obvious unless you had animals in your game. It's not likely that your sister's mods and cc would show up in your game though: that content is stored locally on your computer, not in Origin. So the only way her content would be on your computer is if you and she had a filesharing service (OneDrive, Google Drive, etc.) set up to sync her and your Documents folders.
Still, if the repair doesn't fix everything and/or you're seeing mods and cc you don't want in your game, the fastest way to address it is to move your entire Sims 4 folder out of Documents\Electronic Arts (you can put it on your desktop). When you launch the game, a clean folder will be created with no content. (If you still have access to your saves and mods, which should be in the folder you moved, let me know, because this means the game is placing its user data folder in a different location.) Don't add anything to this folder yet, even your old saves; just look around and see whether the glitches you described are still present. Let me know either way.
