Fence looks great, what about the tree?
Cutting major roots can also make a tree more susceptible to wind
throw, being blown over by high wind gusts.
Ouch... imagine that chunk being taken out of your leg!
I would suggest dusting off the cut and painting the area with a
quality tree paint. While it is not recommended to paint branch
cuts, it is still recommended to paint root cuts. If you can't
immediately locate a quality tree paint, you could use orange
shellac, which is often used to paint the edges of freshly trimmed
tree bark. It has an "antiseptic" quality which helps with the
potential pathogen issue.
Destructive pathogens are already present in most soil,
just waiting for opportunities like this
Maples tend to "bleed" (sap oozing out of wounds) but it doesn't
look like you are experiencing any bleeding, probably because the
Maple is fully leafed-out. If the wound was bleeding, it would make
the tree paint difficult to apply. Maple bleeding isn't usually a
serious issue, but it does alarm people. It occurs most often in
early spring and late fall, when a Maple isn't fully dormant, but
the leaves are off.
It could be several years down the road before "Wanting to cry in
NY" knows the full result of this thoughtless act. In the
meantime, her best course of action is to keep the tree vigorous
through proper pruning and tree care.
Seeding under trees
roots in sewer lines
Manmade root problems