Answer:
Emotional reasoning.
Step-by-step explanation:
Emotional reasoning occurs when Dora decides that she is fat, based solely on her emotional reaction, regardless of any given evidence.
The dress may not even be her size, since it was displayed on a mannequin, but she is convinced that she is fat, even if the size of the dress was much smaller than hers.
Emotional reasoning leads humans to baseless decisions, which most of the time harms them, and undermines their self-esteem and self-perception.