Yes, Janet Yellen has proven herself a Keynesian economist, and that system of economics has not worked in the American economy. The Keynesian economic theory is a nice theory, but the problem is that it is seldom actually put in to place. Leaders, like Yellen, spend a lot in the bad times, but then don't cut back in the good times.
Why would Janet Yellen even be considered as a nominee to the Federal Reserve if she would weaken the economy. There is no hard evidence supporting claims that Janet Yellen would increase unemployment, or do anything else to hurt the economy. Anyone who believes she will are just making rash decisions based on nothing.