Bran did see the sense in their plan, although he couldn't help but dislike Daniel and Ella's involvement. He knew that the man on the roof became a beast during the full moon, and not even Erik's skills would be very successful against a threat like that.
Regardless, he did his best to return her smile. "I'm sure she'll be fine with it... I hope she is, at least. The less interaction Erik has with people, the better."