I too, am very particular about hand quilting thread. It is best to ask the lady what she prefers to work with.
I prefer a heavier weight, like 35W. Valdani is my favorite. I bought a 500M spool of 35wt Valdani thread and I have completed 2 queen size quilts with this spool and I am pretty sure I have enough left to do one more.
But a huge variable to be considered is how heavily will they be quilted? More quilting = more thread.