She is jerkin your chain bro. Very good site to read for new and used selling and buying:
CarBuyingTips.com new car buying guide, avoiding dealer scams, new cars, used car buying
Specifically go here if you want some real ammo.
Fighting Chance New Car Buying Guide - Buy or lease a new car with our car buying guide. Get new car invoice prices for most all vehicles. Buying a car? Don't do it without this car buying guide.
For a reasonable price ($40 i think) they will send you every tidbit there is to know about that new Tundra sitting on the lot. Prices, rebates and dealer incentives, tons of great negotiating tactics, and industry intelligence on the latest sales figures for your car, softening of sales, etc.
Things to remember:
She is never going to tell you what her real cost is. Even at $2000 below invoice, she will probably still make money on the truck because of the "holdback" from Toyota. This is an incentive from the Toyota that goes to the dealer when they sell a car. Typically its 5-10% of the invoice price if I recall correctly. So basically whenever the dealer sells a car, they get money from Toyota.
You need to decide whether or not the incentive Toyota offers to you is worth more, or if the 0% financing is worth more. Carbuyingtips.com has a nice loan calculator that lets you look at 4 different loan scenarios at once. Really nice for when you are trying to decide how to work your money.
Also in response to your second post: the dealer is offering the Toyota incentive OR the 0% financing -you choose -you get either one independent of the deal you make - that is what their ad says. I have yet to see a dealer say the 0% financing is "only honored on deals they make a lot of money on". It is "with approved credit". The fact that you make a deal below invoice has nothing to do with their terms on the financing. Again, she is just jerkin you around. Although they may not like it, there is no reason for them not to honor their ads. I'd point that out.
Plus I'd point out how truck sales suck right now (better words might be used hah) and just point to all the trucks sitting on the lot. Supply and demand. Too much supply right now, not enough demand. Give me a deal lady and makes some room on your lot, get your dealership that holdback!