Hogwarts is a scary place to be.
When a parent sends their child to school, they expect the teachers and the entire organisation to look after their children. We can morph into an armadillo or another weird animal, but McGonagall deserves credit for sticking to something more mundane.
However, we must consider the regulations that govern being an Animagus. To begin with, what are the rules? If she robbed Gringotts as a (literal) cat burglar, would magical restrictions still apply?