Ai-chan shall make a guess! The reason why she said her home is very spacious and the reason why she doesn't want him to walk her all the way home is because... she lives in a graveyard!
It's a good idea to be suspicious of everything but not to the point of being paranoid, especially if it's a rare case like a teenager running away. And for someone who keeps smiling despite leaving her family, that's hella suspicious.