When I need to use LaTeX with matplotlib, I add the following to the python script (+ additional commands for debug info)
import matplotlib.pyplot as plt
plt.rc('text', usetex=True)
plt.rc('text.latex', preamble=r'\usepackage{amsmath}
\usepackage{foo-name} `...')
matplotlib.verbose.level="debug-annoying"
commands to make your plot here