How do you argue with problem solving skills like these?

Yesterday morning I was all set to head out early for some grocery gaming. I was dressed and ready when I approached Lauren about going shopping. She was in "a mood" from the minute she stepped out of her bedroom door and therefore wanted to "assert her independence" at every available moment. Her first reaction, when asked to get dressed to go out, was a very firm, "NO. I don't WANT to go shopping. Today is a 'stay home' day." I told her that I really needed to go to the stores and that I would appreciate her cooperation. She stewed a bit more and then came to me with a proposition...

L: Mom? I have a idea. (yeah that's pronounced, "UH idea")

M: What is it?

L: What if I ride my tricycle to the store? I could ride beside the car.

M: *puzzled look*

L: I could go out and practice in the driveway right now! (very enthusiastic, and already anticipating my answer)

M: Well...you don't have a HELMET. You have to wear a helmet if you ride your trike out of the yard. (thinking this would be an easy out with little argument since we in fact do NOT have a helmet)

L: Mom! I won't fall SILLY! (guffawing at the ludacris statement)

M: I don't think riding your tricycle on the "big road" with cars is very safe Lauren.

L: I can ride it on the sidewalk.

M: You'd have to cross the road to get to all of the stores.

L: *thinking* Well I'll just ride it on the other side!

How do you argue with problem solving skills like these?