I'm sorry she made a comment that hurt your feelings. It doesn't sound like she has ever made a handmade gift for someone else or she would understand how we feel when we are making a quilt for someone we love. Your grandson will be happy with it and that was your plan to start with :-P Enjoy yourself watching him enjoy his new quilt. Take a picture to remind yourself of that and share it with us - you know we would love to see it :P
Non-quilters don't realize the time (how could they?) and heart involved in a quilt. Try not to be hurt by what she said, she just doesn't know any better.