While shivering can be a symptom of fever, it’s not always present, so I wouldn’t consider shivering an important indicator. Many lists of fever symptoms in cats don’t include shivering.
A far more telltale sign is an overall sluggishness and low responsiveness, lack of appetite and possibly dry/parched nose and mouth. If you know your cat, you won’t miss it, even in those very old and laidback specimens with the temperament of an old log. If you suspect something is amiss, contact your vet. Without attempting a diagnosis, I would assume she’s just fine, as you write that her behavior is “quite normal”.
Seeking warmth is a very common cat behavior and perfectly normal, even if cats tend to do it to a degree where we humans question that decision. Here the cats’ ancestry shines through. Our cats are descendants of the African wildcat, who’s habitat includes tropical and subtropical grasslands, savannas and steppes, but also deserts. If a cat feels that their location is too hot, it will seek shade. As long as the cat can freely choose to leave the hot spot and has access to water, you needn’t worry - don’t confuse the hot ears of a cat that’s been sunbathing for a while with the hot ears of a feverish cat. Just observe her behavior and test at a later time.