My male cozmo always has his tale extended but Stella she curls her tale up like a chameleon. Is that normal?

Depending on a lot of things... yes.

Certain types are more likely than others, but it also comes down to personalities. Arthur, my platinum, holds his tail curled up most of the time... but I've been told this is a common trait for plats. My two girls (WFB & classic) will raise theirs are they run, but then they flatten right out. Merlin (BB) is the only one that seems to leave his tail down, but I've read that they're no different than classics in personality.

So... I believe that is normal since traits & personality play into it.

Stella could be a tail carrier. Give them some plastic bracelets and see if they turn up in their pouch.