Most people use an iron on interfacing on the back of the T-shirt front before cutting the squares. You might want to price out enough for the quilt, it can add up. Are you going to need fabric for sashing? How about quilt batt and backing/binding? Do you want to throw in your labour or free or do you want a little for your trouble? Give her the estimate of the cost and see if she still wants to proceed. Most non-sewers have no idea about what fabric costs.