No it is not too much. Tell her to get the person or persons who are questioning it to calculate and bring that much in.
However, before you do that, give them the instructions for adding to the width for the back.
For the 3 1/4 yds you are asking for you will have a piece about 65" by one half thr width of the fabric for your borders which you say the student will need.
Sometime you have to let others discover their mistake.
I would tell the mother that you will need enough fabric for the back for the finished size. and x amount for the borders and then when there is not enough fabric ask to bring more..........
Don't argue with anyone about it but just give the measurements and ask them to get the amount of fabric needed.
And I would not redesign the back with piecing to accommodate the questioners........that would change your instructions for the class and might confuse some students.