Mary S has already suggested that giving a warning each time is not such a good idea - little kids already know that certain behaviors are wrong, especially if they have ever received any negative feedback about it even once, so the additional warnings really do end up training them to ignore you!!
Just a question about using time-outs: why not a swat on the behind??? I've read some of the other suggestions of putting them in the bathroom and holding the door so they can't get out, gates to keep them confined in a room, and so on, and I don't understand how those behaviors are viewed as less cruel than a quick swat and the words "don't do that."
Not to mention the sheer exhaustion of so much negative energy!
The good thing about using spanking instead of time-out is that it is swift, effective, to the point, easily understood, and it's immediately over with so that the child can go on with a happy day -- and you are not spending time trying to figure out how to force a child who is already disobedient to obey an even more unpleasant order of sitting perfectly still for an amount of time.
Part of the negative reinforcement you have going on here is the attention she is receiving: sadly, negative attention is still attention, and little kids who start out being "good" sometimes end up slipping into monsterdom because they get more attention by being bad.
When she is behaving in a way that you approve, whether it is quietly playing with toys or whatever, consciously spend some time with her by giving her a hug, sit with her for a little while, tell her what a sweetie she is and how nicely she is playing, stuff like that. Positive reinforcement. If you do that and eliminate all the time you are spending on the warnings and time-outs then she will learn that it is more fun to be good and get hugs and smiles than it is to be bad and go through all that other stuff.
You will also be happier because all your energies are spent in enjoying your child rather than in fighting to make her sit in a chair or something.