My current package of Mountain Mist says 5 inches for tying.

Was it machine dried on anything other than low heat? When polyester fiber is overheated, it can sometimes soften/shrivel up, similar to how that batting looks.

I have seen this happen with cotton batting too. Also, maybe it was in a dryer that was too warm.

I'm wondering if she washed it a lot. I repaired a quilt for a person and she washed it in very hot water every week! No wonder.

Did you ask if they washed it in hot water, high spin cycle? I had to remind my daughter quilts are washed on a gentle cycle with lukewarm to cool water and use a woolite or a soap for cold water. Looks like maybe the ties should have been closer together too. Glad you'll be able to fix it.

This is why it is important to follow the quilting distance recommendation on the batting package. If there is too much distance between quilting lines the batting will separate and pull apart. If a quilt is going to be tied it is necessary to choose a batting that states on the package that it is OK for tied quilts- not all battings are good for tied. This happens with cotton battings too ( often faster than polyester) if your batting says to quilt every 2" - 4" more is better. Always consider the recommendation to be the minimum.

This can happen for a variety of reasons. One that comes to mind is the poly batting fibers were not bonded , or very minimally bonded. Bonding helps to keep the fibers from migrating and bearding. Bonded fiber battings can be stiff. so it is best to see them out of the packaging. I do wish stores selling battings would have a 12 inch square sample so you can feel the fibers and the structure.
When buying a poly batting check to see how easily those fiber area able to be pulled or stretched. Sometimes when we are getting a poly batting to lay flat in the sandwich construction we break some of the bonding or fibers. Some of the early poly battings were no bonded at all. and washing would "bunch" the fibers since there was no "structure" to keep them in place.

That is why I have never like using polyester batting. When W&N and Hobbs batting came out, I made the switch to cotton batting and never have looked back.

I have seen the same with the blankies I repaired for a friend's daughters. The girls drag them around everywhere and the quilts are washed often. It is shocking to see but I'm not sure any batting would survive the constant use these quilts endure.

This is probably why my mom always used "sheet blankets" for the batting. I wish I could find some new ones now.