I have a pack.mcmeta that's working fine, my functions are in data/cars/functions, and the only tag I have is data/minecraft/tags/functions/tick, all my files have the right endings, and my commands seem correct.
The two things you are describing are somewhat complicated and WILL require you to know how to code. There are very severe limitations to what codeless mod makers can do and you can't expect them to do everything.
If it was working fine before your sister turned it off then I would say that the world got corrupted because the game wasn't able to finish saving or running anything. It's happened to me before. If you were too far along to restart then I would say try using mcedit or something to pull everything out of the world and put it in a new one. If it doesn't work you're just going to have to restart or give up.
Exactly what I was going to say. Just ask Mojang if it's okay. Hope they say yes, I liked those textures and if I delete the ugly ones it would be nice to use them again.
