The lack of foliage at this time of the year does not bode well but the plant roots have developed new shoots that have leafed out. That is encouraging. It is now difficult to guess what happened in a prior year without symptoms of things going haywire. A scratch test may help you tell the extent of life left.

I would suggest a formal soil test since it is a mature, "large" hydrangea tree. Possibly a Pee Gee Grandiflora, not Quickfire. QF stays smaller. The tree may be 30-50 years old. With the soil test, you can check for nutrient deficiencies, high soil salts near the road, even the soil pH...

Maybe the tree needed more water as it got older but compacted soil plus rain + what your sprinkler provided was insufficient. Maybe the soil got too salty or compacted. Maybe the tree got too much water and developed root rot. I wonder if water tends to collect there... perhaps not looking a picture 3. Maybe it was old and winter was difficult. Maybe pests damaged the roots but if true, I would expect that if the pests kill a hydrangea tree, nearby bushes/trees may also have been affected. There is some damage near the base in the last picture but I have no idea if this is old and the tree got over that... or if this contributed to the decline in some way. Hmm, too many maybes.

The soil does look very dry in the last picture. Not sure if the soil drains well in that spot or is compacted. The tree does not seem to have any mulch. The lichen in the rocks in pictures 3, and 4 suggests that the area may be humid enough for the lichen. But then I wonder if the soil humidity got to high enough levels in the soil itself, which may suggest root rot. I guess too much water at some times of the year? I am mumbling to myself now... Hmm, oddly, nothing much appears to be growing near the tree. Somehow, I sort of expected to see at least some weeds since the Pee Gee tree is so near the road and the edge of the property. Signs of a soil problem? Hmmm

Too many questions... After the formal soil test, review the results and see if the tree has either awakened late and leafed out late for some reason but if it has not, you may need to use a scratch test to remove dead wood and continue with the smaller stems now growing at its base.

When you cut into a branch, is it green or brown inside? If brown and brittle, it is dead and should be pruned away, It is attempting to regrow from the roots, but it will be a bush, not a tree when it does.

Luis,

Thank you for taking the time to give your thoughts and suggestions. A soil test is a good idea and I will raise that with her. I am going to their house this weekend with pruners and loppers and I will see what’s alive and dead. hopefully it’s waking up late, but that wound at the base and the lessened growth doesn’t bode well, as you said. Such a shame, as it is (was) a beautiful mature tree!

Calli,

That was my first suggestion to her as well. We shall see! Hopefully the tree form can be saved.

Shay