Mokushiroku no Yonkishi - Ch. 94 - Incident on the Night of Prayer

[MangaDex]

 

[HDMI1]

She's either with the pacifist Demons they met earlier, or Zeldris sent her as support since Arthur would go after the Demon Realm after he takes over the planet. Maybe she's Zeldris' daughter that he had with the vampire chick.

 

[Dvv]

Would

 

[HyoEden]

Well, she's there because Arthur tried to change destiny, as Guinevere warned him; And they also confirmed that the Camelot Knights weren't aware of her.

On the last panel we see Tristan taking a more defensive position after she revealed to be a Demon, but she looks slightly disappointed, I mean, she just told her that she was not on Camelot's side, and he still treated her as an enemy, just because she's a Demon. (Even thou Meliodas is a Demon himself smh).