This is why.  She presses Treasury Secretary Tim Geithner on the Constitiutional authority for the Treasury to give out TARP money, apparently not understanding that Congress, of which she is a member, passed a bill which provided not only the TARP money, but the authority of the Treasury to dole it out.

In an interview with after the hearing, Bachmann said, “My intent to the line of questioning is legitimate because I have a number of constituents that ask me ‘Can they do this?’”

Geithner is understandably confused at the stupidness of the question.  It's kind of like asking "Where in the Constitution does it say we have to sit on chairs?" 

Still Geithner answered the question, saying "the laws of the land, of course", which is technically correct.  Article I, Section I grants Congress the right to legislate, and the TARP funds were legislated to give authority to the Treasury.  Article I, Section 8 would have been a good answer, too.

Bachmann also asked if the United States was giving up the dollar. “I’m wondering would you categorically renounce the United States moving away from the dollar and going to a global currency as suggested this morning by China and also by Russia, Mr. Secretary?”

Of course, China and Russia were not advocating a "global currency".  They were merely suggesting that the international community use something other than the dollar as its reserve currency.