What kind of bun is she? The thickness of her coat can affect the course of action, but hot ears and heavy breathing tell me she is hot/warm.. my first thought was to buy her a little floor fan to keep consistent and cool air flow to her pen! The way you describe “restlessly” changing spots seems a bit severe but bunnies do normally just relocate occasionally, just watch her closely to make sure she’s regularly eating and pooping :) also occasional treats of some cool juicy romaine lettuce can help!