Chelsea dressed in torn jeans and hoodie when she gave a speech to the rotary club asking for donations to the humane society. the audience did not find her to be credible and did not donate much. what speech element was at work here?

The correct answer is ethos.
Ethos is the appeal to ethics, and it is one of the means of rhetorical speech where you try to persuade your audience to believe your credibility. Obviously, in this case, Chelsea didn't manage to do that because the audience did not find her to be credible enough, which is why her ethos in her speech failed.