When Tritan said that Elyna could just stay in her room, it meant that she was really not allowed to leave her room at all. All her needs were brought by the maid. Tritan also visited her every day, although Elyna just ignored him every time.
Elyna felt stuffy. Not only could Elyna not escape, but she could only drink blood to replenish her energy. Elyna was afraid of herself when she first consciously drank the bloodstock that was provided especially for her. But every time she almost fell because she couldn't eat anything but blood, Tritan would personally help her to replenish her energy.
When that time came, Elyna would lose control of her own body and start eating blood as if it were the most delicious food on earth. That made Elyna even more afraid of herself. Elyna was afraid that she would lose her werewolf side. She was afraid of losing her relationship with Val because of Tritan's efforts to make her leave her wolf side.