@Ncararc Seeing how she's following him around actively all the time and not basking in the sun or next to a heater, she's warm-blooded. Typically when you think of how dragons are in fiction, the behavior resembles a warm-blooded creature. Birds (dinosaurs) are also endotherms, as were pterosaurs. Cold-blooded animals are quite mentally dull compared to warm-blooded ones. History also doesn't know of large actively flying ectotherms. Gliding in the air is a different thing, but dragons are typically masterful fliers, only beaten by the likes of griffin in some tales.
Funnily enought if she was cold-blooded and her place of isolation had been cold, she would have barely noticed 300 years passed.