How wide are her typical projects? I'm finding there is a quite thick batt (and it is a tad too thick for me who likes them thick) that's about the width of a twin that I can get at Joann as yardage (not prepackaged). I can get the info if that will work. I prefer less quilting and a thicker batt than is currently popular, which tends toward Warm & Natural (which is soooo heavy to me) and heavy quilting.
For my queen sized projects I bought a close out roll from a discount site on line that I'm pretty darn happy with, but it isn't anything I can get again. I think it was end stock from a commercial run. Extra wide and something like 25 yards delivered for under $150 but it was a risk, happy it worked out for me. I do a lot of donation project so it would have been used.
Batting goes by the weight, but you also have to look at the size of the batt, I wish there was a better standard like weighing a square yard/meter. Anyway, if you go to Walmart and look at their "thick" pellon it looks pretty good on line and the weight seemed good, it was much less in person, could read through it. That weight was along the 108" width, it would have be thick at 48" but not double that. No offense to the stuff, I know some people like it a lot but I'd be like your Aunt.
Here's a couple of projects using that batt that's a little too thick for my tastes.