I think it's completely valid to either A) Set a boundary here, or B) As to have it moved so you can go as well.
There is no reason to allow her to go on a date with someone she hardly knows. He doesn't have any reason to set up this little drinking date with her like this to "catch up" when they're not friends.
I don't know why people in this thread are acting as though it's completely normal or reasonable and that you have to turn a blind eye.
Let her know you're uncomfortable with it. He reaction to just that will tell you a LOT, and then go from there. Do you want to go too (choose another time) do you just not want it to happen (it's weird, he doesn't need to ask for her time like that) then she doesn't go.
Boundaries are okay. If we flipped the genders women would be all over this thread saying "woahhhhh girl, boundaries! woah girl!! nope!"