At 4 I sat in the room and "helped" them clean it up. I would say, OK get all the Lego's and put them away. Or all stuffies, dolls, books, etc. We made a game out of it.
If she has too many toys take some away.
Make sure everything has a place, stuffies are in a hammock or on the bed, Lego's have their bin, trucks go in another, Barbie's and paraphernalia.
Make sure the bins are big enough.
Responsibility is taught by watching parents be responsible. If you are responsible for keeping the rest of the house clean they will want to emulate your habits and keep their room clean. But if your "rooms" are a mess why should she keep hers spotless? (I know she's only 4, she will be 14 soon enough though.)
For years my son has had to be reminded to feed the dogs, he's 11. Now he will sometimes go down and feed them without me asking.
THey have to do chores, I still have to remind them, but I have been surprised lately that when they want to "make", cookies, cakes, dinner, the kitchen is usually cleaned up. MIne are much older than yours, 11, 14, and 16.
My best friend was pleasantly surprised when her son called to complain that SHE made him early by 10 minutes for every function, event, whatever. He is 23 and gets super riled when someone makes him late.
This all starts at 3 and 4. Yes, she should clean her room, but you should also sit in there with her and "help" her. That doesn't mean you do any work, just sitting on the bed and giving positive reinforcement should help alot.
Think of it as a lifelong process.