We all know how this works.

I got chatting to a girl online and we've got stuff in common and she's keen to join me /out/ for a day.

I have no idea what fitness level she is nor whether she even has suitable shoes for a day hike. I don't want to freak her out and make her think i'm some special forces wannabe but I also don't want to end up breaking her.
What sort of distance should I plan for?