That 'if' seems to shift the atmosphere of their conversation. She can't put her finger on exactly how it shifted, but his words...they just feel so final. It's tugging at her and that is bugging her.

"You don't have to. You asked where to get something to eat, I showed you it really isn't that big of a deal." Unlike how she flat out told him she doesn't eat with demons, this is said more like one would tell a grateful stranger they don't need to pay them back for the dollar to make a phone call. It really is fine the way things are. No payback necessary.