I just finished my first quilt too, only I hand-quilted mine. As much as I love it, I can only imagine how upset you must be!!
If it's not truly horrible, I would try washing it and see what it does. I could hardly see my stitching after washing & drying mine. Mine was supposed to be for a brand new great-niece - now if I can only get our niece to e-mail me back with her address, so I can SEND it to her! Otherwise, I might just keep it myself!!
I had no idea that you could rent a longarm machine and use it - how would I go about looking into this in my area???
My sympathies for your quilt baby, and all my hopes that she can be fixed!
p.s. I finally found where you had posted the pictures of the quilting. Oh. My. Goodness! This IS truly horrible!! I know it would be horribly difficult for me - I hate confrontations of any sort - but maybe get someone (another quilter!!) to go with you, and yes, this lady needs to be told that this is NOT professional grade quilting!!!