If you are using a printed pattern - or one designed by someone else - just "their" requirements and go from there and tell "whoever" that this is what is needed.
Have you made a "practice one" to make sure it will work?
I think 3-1/4 yards is going to be skimpy - especially if the fabric is less than 45 inches wide (after washing)
Are you able to go with any of these mothers and/or students when they go shopping? Is this mother looking at the most expensive fabrics available?