People that do not quilt have no idea what it take for us to create our works of art. Unless it had deep sentimental memories I would tell her you are not a miracle worker and give it back to her

Run, really fast and far. I am not a great quilter and would be terrified to attempt making a commissioned quilt. No way would I attempt to repair something. I think the words "this is to far beyond my expertise but I thank you for having enough faith in my ability to ask me" would suffice.

If you're making a new top, why use old batting and an old backing? You'll probably be faced with replacing the batting and backing in the near future.

I took old quilts that my grandmother made and cut them up into little bears - all tattered and torn and perfect. My mom, her brothers, and their families will all be able to remember her and her quilts.

if you would not enjoy doing it please just return it to her and let her know. Maybe she loves the quilt and wants it restored. It would be terrible for you to decide to just remove/replace the top if that is not what she wants/ expects. If you have no desire to work on it , it would be best to just let her know. If you ( might not mind) then talk to her about it, find out what her hopes/ expectations are. Best to never (Assume) what someone else has in mind- communication is always the best way to proceed.

I would not attempt to fix it. I only like making new quilts.

My grandmother used to piece quilt tops from scraps she received for free from a hat factory in the area. She didn't realize that the fabric was very poorly made. It did not hold up well at all, and soon began wearing through. These were not heavily used/washed, either. Just the poorest quality fabric, probably not even available for consumers. In the factory, I think it was bonded to a stiffer backing, for the hat construction. She just used it because it was free. A pity, all that work didn't last.
My point is, some old quilts are not worth saving. And, I appreciate good fabric even more now.

IF she is willing to take the stitches out of the top, you can possibly make a small wall quilt out of what remains. Or teach her to do it. Deconstruction takes a lot of work, weeks in my case, and of what sentiment would a copy be?

A quilt made by Rob's grandmother came to me, and once I had enough whole pieces to do something with, I backed them with the finest thinnest inner facing, which gave me some good edges to cut and reassemble.

I think I have some photos

That is awesome! I can do that with the quilt my mother made for me when I was a small child! I have the shreds in an acid-free box, not wanting to let it go!

If she bought and it has no sentimental value, maybe offer to make her a brand new one using the same pattern. That would probably be easier in the long run.