Dealing marijuana. "Pushing" means drug dealing, and "tea" means marijuana.
"My daddy beats my mommy, my mommy clobbers me, my grandpa is a commie, my grandma pushes tea, my sister wears a mustache, my brother wears a dress... goodness gracious that's why I'm a mess!"
-West side story song Gee Officer Krupke
the grandma is pushing tea, so she deals marijuana. badass grandma.