old Girlfriend needs her mother permission to travel with me !!

This was my first thought as well.
I'm also kind of curious whether she really wants to go or perhaps she's a little uncomfortable with the thought of going on a trip together having just become exclusive not long ago.

Perhaps she's using this as an excuse because she knows how much op wants her to go and she doesn't want to hurt his feelings by saying shes not comfortable with the trip.

Of course this is speculation because we don't know how intimate op and his gf are and how comfortable they are around each other. Just my thoughts.