3 year old driving me insane

She needs a routine.
She needs to know what is going to hapoen on the days you are at home and on the other days.
Yes, it is perfectly fine to give her small chores to do.
And talk her through everything the evening before and at the end of the day before she goes to sleep.

3 is a tricky age - I found 3-4 by far the hardest time. Hang in there because it gets better.

Something I found really helpful for constant snack requests was to give my son much more control over this. I set up a box for him that was his day's allocation of snacks, and then I told him he was in charge of when he had them, and that he could get them himself any time. It was all stuff I'm happy for him to have but I placed no restrictions on it except to tell him that once they're gone they're gone, until the next scheduled refill.

Naturally for the first few days he blew through them instantly, didn't eat his lunch and was whining for more by early afternoon. But within a week he adjusted and now he helps himself when he actually wants them, but also paces himself so he doesn't run out too soon. He actually snacks less now and it has completely removed from my life the stressy battle of always being the one to decide yes or no about snacks, and I don't have to be the snack butler.

Any other areas of her life in which you can cede control while still being safe, I would go for it - whether that's letting her choose her clothes, making her toys more accessible so she has free rein, etc. Three year olds think they are so desperate for control, that if you can give it to them in small ways it can take a lot of the heat out of your day.

Hang in there - she'll come through this very difficult age one day, and a nice mellow four year old will be waiting on the other side!