Afaik, no set convention about calling the females regina can develop, because at the time of typing, only one female tyrannosaur has ever been found in good enough condition to confirm her sex. I think we would need lots of known females to see that linguistic change happen.
Not even the way it works anyway, afaik. Gender is not sex, as we're so fond of saying. An animal's name (or a human individual's occupation) can be masculine or feminine, independent of their sex. Both in actual Latin, and biological nomenclature.
Rex/regina is a bit different than just gender though, in that they're a sexed pair. Sort of.
"Rex" is not necessarily "king", it can be "ruler". Whereas "regina" is specifically "queen".
It usually gets translated as "king", idiomatically, so "Herodes rex" -> "King Herod", but to always do so is a kind of sexist assumption.
I sense these sort of things are a bit unstable in male-dominated areas. When there's only one word, there's an urge to make a "female" form with a suffix, to escape the male-default assumption. When there's a pair of such words, there's grumbling and an attempt to recombine them to prove equality. And the pendulum swings. Like "actor/actress"; and I think "rex/regina" is similar, and unlike "king/queen".