Love the tshirt quilt to be!
When I use a new to me quilter I try to see examples of her work first. I ask if she does free hand work, computer guided or just all over stitching. It makes a difference to me so that I know what to expect in the quilting.
Also make sure you specify the color of thread (just made that mistake on my most recent quilt), and if she is providing the batting what she would recommend for the look you want. For example if the quilt is a child's or baby quilt I wouldn't want flat Warm and Natural batting but a nice poly with a bit of loft to make is a bit fluffy. On the other-hand if I have a "vintage" type quilt quilted I want a nice 80% cotton for that flat antique look.
Hope this helps and just make sure that you and your quilter are on the same page as to the look you want along with the price and other details!