If I get what you want, then there should be no problem. I would use Albums to make it even easier, since otherwise pictures with the same dates could get all mixed together.
You would select the pictures you want to send, and then (…)> Add to Album> + > name a new album. Then select all the pictures in that Album and AirDrop them to her. She does the same with her pictures. The Albums don't get AirDropped-- just the pictures. You could select the pictures you get and add them to the Album, and then you'd have all the vacation pictures together.
I suggest the Album thing especially to keep the owners' pictures easy to select without having the others mixed in.
Hope this works for you…