Isn't she being a bit too cruel to ml?

I feel the same too but she had to make some distance since she's only an 'extra' that would die in order to go back to her former world

She has to be more cruel because she thinks that the reason she was sent back in time, instead of sent back to her world, was because she was too kind.

That caused him to become a softie instead of the tyrant from the original novel, meaning she didn't play her role out the way she was supposed to.