To be honest, I wanted to switch to Tanya too in my TL, but I wasn't sure as Titania is the novel translation.
Tanya is the correct translation if you directly translate each word into romaji, then it's Tanya. "ターニャ", "タ" is Ta, "ー" is like a pause or silenced note, "ニ" is Ni, "ャ" is ya. Hence Taniya, but if you put the Ni with the Ya together, it would become "Nya", similar to what authors uses to mimick cat noises, basically Japanese's "Meow".
But, I am assuming what you read was the novel TL like me, then in that case, the original TL translated her name to Titania.
For the other chapters in this manga, maybe some translators used Titania(Not sure), and some used Tanya(Chapter 0), hence it's just a preference, or as a matter of fact, maybe it was always Tanya all along, as when I checked chapter 0, she's called Tanya there, and I don't wanna read every chapter again to check if her name was mentioned.
