Can you have them call this person and explain to her that however it happened her shirt did not make it to you on time as you have already started quilting on it and you really don't want to take a chance of not getting it sewn in very well. Explain if they had gotten it to you before you started to quilt it you could have included it lots easier. Have them ask her if she would mind it being on a pillow case( which can be set on top of the quilt) or on the back with/on your quilting label. You could put it on some muslin and have your info going around it with made and quilted by, for charity, date. Just a thought.