All right, so bringing her your quilts goes a long way toward making your longarm quilter happy but there are things you can do to make her even happier with the quilting you bring her way.
Before I owned a longarm I heard the requirements for the quilts I took to a longarmer and I followed them, but it wasn't until I started quilting on a longarm myself that I really understood why they were asking me to do certain things when I was preparing a quilt for quilting. One of those was providing a backing that was 2"-3" larger all around than the quilt top. It isn't just to make you buy more fabric or to sometimes seam the backing.
Recently I was given a top, backing, and batting to quilt for Project Linus. I think the pattern must have been designed with the assumption that the backing would be 44" wide, but it was not and there was, at most, 1/2" around. I could have basted some extra strips of fabrics to the sides and sacrificed a bit of the outside border of the top but I thought it might be a good chance to illustrate the reason for the extra 2"-3" around on the backing. (And the baby quilt was small enough that it would be less time-consuming to correct what the 1/2" wrought!) I hope that the photos and description will help to illustrate.
If you've seen a quilt loaded on a longarm frame/table you've probably noticed the clips that run, on straps, from the sides of the frame to the edges of the quilt. The purpose of these is to stabilize the edges of the quilt so they aren't "flapping in the wind." The clips need room along the edges to clip to the quilt. They don't have to take a large "bite" into the quilt, so why more than a half inch or so?
The longarm machine has a base, or bed, that is several inches wide on either side of the needle and anything that is in the path of that part of the machine has the potential to stop or impede the flow of the machine and, therefore, the quilting. Even a small bump can cause a blip in the quilting. If there are a couple of inches there is room for the machine to navigate around the clip. (Below you can see how the edge of the machine bed is going to hit the pony clip underneath.)
When the margin is as small as the 1/4" - 1/2" that I was working with, the edge of the clip was right at the edge of the quilt top so I couldn't quilt in that area if the pattern called for it be quilting there. My longarm is hand-guided, so I if I'm watching I can try to manually account for that and adjust and hopefully, being at the edge it wouldn't be TOO noticeable. (I can guess that it would be more of an issue on a computerized machine, as the computer can't see the problem coming up and make a correction for it.) Here I've cut away the batting to the edge of the backing, so you can see where the edge of the top and backing are, in relation to the clip. The hopping foot is bumping up right against the clip, which means I couldn't quilt to the edge--and the clip is barely holding the edge, which isn't as stable as I'd like, and puts extra strain on the edge there.
I could plan ahead and move the clips so they fall where a part of the pattern doesn't. However, that can cause problems of its own: without anything to stabilize that edge, the tension is all over the map. Here, on the back of the quilt, you can see a star at the edge from which I'd moved a clip, so I wouldn't run into it with the machine.
Next time you prepare a backing and top to take to your quilter, be assured that she will appreciate that margin around the backing, and be able to do a better job for you.