Limelight Hydrangea. Why the leaves on the bottom are turning yellow all of a sudden with brown spots

That landscape fabric she has is pretty much one of the worst things you can do when you plant panicle hydrangeas. It not only keeps excessive moisture around the roots which then cannot evaporate, but it also prevents the exchange of oxygen and carbon dioxide, allowing carbon dioxide to build up to harmful levels in the soil. I would recommend that they remove the fabric for a good 18″ circle around each individual plant – they can also just cut an X shape and peel it back, it doesn’t necessarily have to be a circle. Once they do that, this should abate, though some damage has already been done so it may continue for another couple of days. The yellow leaves can be removed…this is a cultural issue, not disease.