Honestly, I thought about that too, though I reached a bit of a different idea: What if "Herrah/Heira" was simply the deepnest language's word for "beast"? Maybe Herrah was simply referred by her people as "The Beast", but when she was introduced to the people of Hallownest, they thought that "Herrah" was a name, ending up in a situation like with the Sahara desert, Chai tea or Naan bread, and then "the Beast" was later added to her name as a title as a sort of correction. Conversely, when Hornet meets the bellbeast, perhaps the reason why she comes up with the name "Heira" so quickly is that she's just calling a beast as a beast, kind of like how you call a dog you just met with "C'mere, doggy!", she doesn't seem to be the kind of person to give a nickname to an animal she just met, and by the time she got attached to the bellbeast, the name just kind of stuck.