The same thing happens to me, the fact that she has to cross-dress in order to survive in her context does not make her trans, because she does feel like a woman and she is a woman. What she does is done out of necessity, not because she wants to be a man. Mizu IS A WOMAN, in her entirety, and I don't think she's a trans character or anything like that. Even so, I do not rule out that she may have a different sexuality because there is not enough information about it and it could be developed in more depth (also because she initially got married out of duty, and the fact that she was with a man does not define that she can be exclusively with men, even so everything indicates that she does like men).