What does this woman being threatened by the snake represent

I believe you are referring to the famous political cartoon created by American cartoonist Joseph Keppler for Puck magazine in 1881 and titled In danger. Puck. "What are you going to do about it?" In it, a large snake, which represents monopolies involving U. S. senators (the word monopoly and the names of various senators are written throughout its skin), has its tail wrapped around the dome of the U. S. Capitol, as if suggesting that it controls the U. S. government, and, menacingly, faces a female figure that personifies (or represents) Lady Liberty, while, to the left of this female figure, Puck (a personification of Puck magazine) asks Uncle Sam "What are you going to do about it?"

The personification of Liberty is a representation of all Americans, who are threatened by the tyranny of the monopolies - if the government does not prevent it. In the years where this cartoon was created, the telegraph and the gas industries, among others, were controlled by monopolies that charged ridiculously high amount for their services.