[@Menhir] Even so, it just seems like a silly excuse not to join up. You're in control of when your character arrived at the post office and how long she's been traveling relative to when everyone started walking up the mountain. You're in an ideal position to time skip. Technically, you've been in an ideal position this entire time since nobody else has interacted with Layla yet.

"After hours and hours of traveling, Layla came upon a group of three people."

"After hours and hours of traveling, Layla came upon the school, seeing right away that she was a little late."

This is a pretty basic tool for roleplaying-- not a new concept. I mean, I don't mind if you don't want to join up right away. If that's what you want, then by all means go right ahead. Just say so in a straightforward fashion and don't accuse me of making it so Layla couldn't join them.