Barbara was really shocked when her candidate was not elected. she had assumed that everyone felt as she did and supported her candidate's ideas. this is an example of

This is an example of false consensus effect.
It is a type of bias where a person overestimates his or her opinion - they might think that the way they think is the way everybody thinks about a particular topic. In the case above, Barbara had a particular opinion about her candidate and she thought that everyone shared her opinions, which was not the case.