The logical fallacy used in these lines is a <u><em>red herring</em></u>because <em><u>the mention of her skill as a musician is irrelevant to whether Sally would make a good president.</u></em>
A red herring is when one point is presented to try to distract you from another. To distract you from her being good at debates, the person says she is bad at playing the sax (which has nothing to do with being class president).
This logic is incorrect because they're saying Sally would be a bad class president because of her instrument playing, which doesn't have anything to do with being a class president. It mentions she's good at debates, so there's a good chance she would be a good class president.