I’m a HCP and regularly listen to peoples chests, examine them, etc - I will generally ramble niceties and reassurance when I examine children as they’re often very nervous, and try to move through the examination as fluidly and casually as possible, so I’ve checked everything before they’ve really even realised i’ve done a great deal. So while I do the examination I’ll chatter away to them in this soft and gentle, sort of continuous motherese, along the lines of “I’m just going to have a little listen to your chest, is that okay sweetie pie, lovely, shall we get mummy to lift the back of your top up for me, good girl, this might be a little be cold on your back, there we go, nice work, you are so brave, let’s just pop this little machine on your finger, lovely, can I check your temperature, brilliant, there we go, all done”.
So I definitely use “good girl” sometimes in my clinical practice, and I’m sure on a particular busy day it could slip out to slightly the wrong age patient. But I’m a woman, and if another woman said that to me accidentally - I’d probably take it in the warm and motherly way it was intended (whether chronological age made that a bit odd or not) - but from a man to a woman/girl - I agree that it has some different connotations or possible extrapolations.