Playing with Saber in this context can be a bit confusing for those who are unfamiliar with her.
At this point in her history, Arturia has already removed the sword from the stone-- however, she is not quite yet king. She is a feudal lord at the moment, and her father is still alive.
Upon becoming king, she embraced that identity as something different than being human. Thus, being referred to by male or female genders doesn't offend her on a level of gender identity as she believes herself king regardless of the state of her vessel-- so this isn't where you have to worry. However, in order to ensure her place as king, Merlin urged she cloak her identity and she obliges. Thus, at this particular canonpoint, she answers to the name
Arthur Pendragon and answers to male pronouns.
I'll be writing her action spam with female pronouns to make things less confusing, but she will refer to herself by male pronouns and as King (Lord for now, but she knows she will become king). It's a bit of strange concept to some, but think of her as accepting the concept of king
as a gender, and it may be a little easier to understand. She
does not reject her body (as she believes the enchantment of the sword will support any flaw she has) or have any such trouble and she doesn't share the same problems as say, Naoko from Persona-- it's a very different situation and she
does not at all feel forced to do what she is doing. Saber's entire life revolves a lot around choice.
In her legend she is said to be very
convincing. Obviously her character design seems to betray that, but her people blamed the fairness of her face on the fact she is protected by fairies and because of her eternal youth; she stops ageing after pulling the sword from the stone. It may seem very "Clark Kent-Superman", but she is supposed to be believable. That said, if your character is particularly perceptive, they may be able to see through her. However, Saber will take any indication that the state of her body is a detriment to her existence as King or Lord as an offensive statement. Otherwise she does not view either pronoun as offensive (though she may still wish to hide her biology for the sake of her people), and even less so later in life.
( important evidence from the wiki )