If she is serious about binding the photo paper directly, here's what I would suggest.
First, determine which size paper you want to use, based on the desired overall dimensions of the bound book. Then, make mat-like overlays that you can tape to the top of your existing easle that have appropriately sized image gates for both vertical and horizontal orientations. The gates would be positioned such that the image would be centered on the net space of the page (overall dimension less the binding margin). If you want to get fancy, you could use registration pins (used for graphic arts, separations, and such) to position the overlays accurately.
Thus, you'd set the degree of enlargement, compose, focus, etc. with the overlay in position, turn off the enlarger, insert paper, drop overlay, expose, and develop.