She's going to keep testing you. And you know she's going to keep pushing at you because she doesn't think you mean business as she already knows that she's been able to get you to spank her. So whatever you do, don't spank her.

What is all in her room that is making it a mess? Is it toys, clothes, both? You could always let her know that if things aren't picked up and put away, that she'll lose the ability to use them. Then, when you have to clean her room... take away some of the clothes and toys that were on the floor, and put them somewhere that she can't access. Eventually she'll end up wondering where things are because there will be less and less in her room. If she wants them back, tell her she'll have to earn them back by helping clean extra things since you had to do her share of cleaning her room already. (My mom once "threw out" a bunch of our toys... it was horrendous seeing her throw them out. It was the first and last time that we ever didn't clean our toys as she made us take them back out. Don't do THAT, but you can let her know that she no longer has access to them until she starts doing her share.)

Also, she likes to watch tv quite a bit right? Is there any chance that you'd be willing to cancel your cable/satellite if she consistently goes to the TV instead of engaging in anything else? (Just a thought.)