Do over. Sorry. That will be inconvenient and with low ceilings a cramped and hemmed in feeling will result.

are you sure they were a mistake?

if your mother in law is short(er), and not planning to move any time soon, the lower height is a great gift to her.

if she is tall, well thats different.

I have an old house, and the cabinets are lower on the wall. There is only 14" of clearance between the counter and the bottom on the cabinets. It looks fine as the ceilings are 10 feet. I'm short so it's a bit easier reaching in, but I still can't reach the top shelf as the cabinets are long and go all the way to the ceiling. However, it is frustrating that my coffee maker and Kitchen Aid do not fit underneath. The toaster fits while not beng used, but I have pull it out when using it or the bread hits the cabinets when it pops out. So you might want to reorder.

Sounds like a redo with the cabinets and the brother in law both.

You should have had a KD do the design. Not a contractor. Or a brother in law.

I *hate* having less than 18 inches under wall cabinets -- anything you store along the walls is hard to use and looks crowded (think mixer or toaster or knife block). Much better to add wait time and get proper spacing. Bummer.

I am remodeling and recently discovered the area above cabinets was not 18" but was 15". I actually like it a lot because I am on the short side as well so those extra inches lower make a big difference in accessibility.

I haven't had issues in terms of feeling claustrophobic or impeding functionality. Everything except my tall coffee maker fits under the cabinets and I do have an area above the dishwasher and sink which has no upper cabinets so that's where I keep the coffee pot.

I was contemplating having my cabinets deliberately lower during this remodel but couldn't do it because of symmetry issues - but other than that I would have done so. I would consider this to be a serendipitous event :-)