Either this is just bad writing, or there is way more to the story than we have been shown so far.
For a girl supposedly hated by everyone, the servants seemed awfully concerned when they found her injured by the guard dog.
The servants who were nursing her back to health seemed awfully concerned about whether or not they were hurting her.
Why would the King and Queen demand that she be healed, only to have her beaten?
Why would her mother, who supposedly cares nothing about her demand that she be brought before her after she was healed, just to slap her and send her off to be beaten?
Also, why would the Queen demand she be healed, only to send her off to the West where everyone expects her to die?
So, she must be important to the Queen for some reason. Either it's because she has some sort of power, or will be useful as a pawn in the future, or it's because the mother actually does love her.
If it is the later, I would speculate that the Queen had to make a deal with the King when Tara was born, to save Tara's life.
They said that when Tara was born, the King threw her into the crib, seeing that she was not his child.
Perhaps the Queen bargained with the King to spare Tara's life, and promised that she would not allow Tara to think that she was royalty.
Like I said above, why would the Queen demand that Tara be healed, just to have her beaten? Why would the Queen even bother bringing Tara before her to slap her, when she knew she would be beaten?
It's possible the Queen begged the King to let Tara be healed, and he said, in exchange, Tara would be punished. Maybe the Queen demanded to see Tara after she was healed, just to make sure she had in fact been healed. The slap could also have been a warning not to trust anyone else in the palace, like those kids who tricked her.
Perhaps the mother eventually sent her away from the palace in order to protect her. If the mother wanted her dead, why didn't they kill her at birth? Why didn't they just let her die of her wounds from the guard dog?
If her mother wanted to just send her away, why did they wait until she was this old to do it? Seems more likely that the mother wanted to keep her near her at the palace, but after it became clear that other people in the palace were tying to get her killed, she decided to send her away for safety. If they just wanted to get rid of her, couldn't they just kick her out on the street? Why send her to a rich castle, where she ends up being treated like royalty?
Why did the mother even bother bringing Tara before her to tell her she was being sent away? If the mother really didn't care about her, she could have just had the maids drag her away without even talking to her before she went. Maybe she wanted to see Tara at least one last time before she left.
Considering all the talk about the Master of the West killing her, he certainly seems to be treating her well, and the butler was even amazed that he let her live after going into the main building.
Perhaps the mother knew he would treat her better.
It just doesn't add up that no one at her birth palace cares about her, if such effort was put into saving her from dying after being attacked by the guard dog.
Another possibility is, that they are afraid what her biological father may do if they let her die. However, wouldn't treating her so horribly anger him as well? If that is the case, again, why does her mother keep demanding she be brought in front of her. If all they care about is keeping Tara alive, they could have pretended she wasn't even the daughter of the Queen, and the Queen wouldn't even need to interact with her.
Also the assumption is that the Lord of the West is her father, but he doesn't even want to claim her.