Several thoughts. First, it's not possible to "reason" with a toddler, no matter how smart you think she is (every parent thinks her child is smart). So don't bother giving long explanations when you discipline her - just a few simple words.
Next, once kids start doing something in particular (pouring her drink on the rug), I don't know why, but they keep doing it. (Any store that my kids have ever needed to use the bathroom in before, they think they need to use the bathroom in that particular store every time we go, even if they just went before we left the house - so if I know that they really don't need to use it, then I don't let them; it's just an association). I wouldn't give her the drink again. If it's juice or milk or some sugary drink, I would stop entirely. If she's that young, why not use a sippy cup that she can't dump out? My kids have a disorder such that when they drink milk at the dinner/breakfast/lunch table, they dump it over about 50% of the time (ha ha, but really they do). So, I give them water to drink. And for some reason, they only dump that over about 5% of the time. Or else I give them about 1/4 cup of milk in their cup. My kids get plenty of milk, by the way, in pancakes (I make from scratch all the time) and other foods, and when they get their 1/4 cup at a time; not to mention that I'm not entirely convinced that cows milk is all that good for us anyway.
Next, if she's making messes, you may need to childproof much better. Spend a few hours putting up or away everything that you absolutely don't want her getting into, or put child locks on cupboards and such. If it's out, it's fair game, and it's not fair to her to not have free access to whatever is accessible to her. That is how kids learn, by exploring and experiencing their surroundings. If you do this, then you don't have to spend the day saying "no", which she has probably already tuned out. Leave a cupboard accessible to her that has wonderful play things such as cottage cheese cups, a wooden spoon, an old pot, etc. She'll be the smartest, happiest kid around. Then you don't need to spend the day disciplining her instead of enjoying her.
And, when she really does do something unacceptable or unsafe, make the discipline count. Absolutely put her in her closed bedroom for 15 minutes. That will make an impression! Obviously what you've been doing doesn't work, so you need to try something else. I think she's too young to try that nanny stuff on her, and in my opinion, I shouldn't have to punish myself to give proper discipline. By the way, pulling the books off the shelf is not naughty, for example - it's normal -put them back once a day, or put them out of reach if you can't handle that or other things like that. Things she could make a mess with should be completely inaccessible to her.
I think you're making this too hard for yourself. It really works to do the major childproofing, and makes everyone's life easier. Also, John Rosemond has an invaluable book called Making the Terrible Twos Terrific. He goes over all this stuff, and says that the terribles start around 18 months, so she's right on target. Do yourself a favor and read the book. Good luck!