Tear couldn't sense that with the boy. He looked and appeared like a human child, so there was no way she thought he would pose any danger to her per say. That and if he wanted to do something, he would have, if Tear assumed correctly.

"Yes, when I travel, there are always monsters between each location, but they at least stay outside of the towns,"

She replied to his question, and taking his comment about there being no monsters. Her guard might have lessened a bit, but it didn't go away completely.