Sink is two bowls, so 2 drains, garbage disposal on one. I can do the faucet; not worried about that (installer drills the holes). Not getting new cabinets, just counters. And the sink is on a peninsula, so don't have to get in the wall. The installer will install the sink in the granite, but won't hook it up to the plumbing. We're supposed to wait 24 hours to do that. I'm thinking it would not be a good idea to attempt myself?

This is an old thread but it helped me. We had a leak under the kitchen sink, somewhere. There's a leak it turns out on the hose for the sprayer. 'kind of where it forms a 'U' near the weight. We have a Kohler K560 CP. (one handle for hot and cold) For some stupid reason I shut off the hot and cold valves under the sink. But it was nice that after 3 years they were not frozen at all. So im using a bucket under the leaky line until I get the replacement hose. ANYWAY, when I turned on the valves and the faucet, hot did not work at all, and cold worked normal. And then I lost some pressure on the cold. So I eventually tried what was recommended in this thread. I shut off the hot valve under the sink and I detached the hot line at the valve point and put it in a bucket. The cold valve was open, and I opened the cold full blast at the sink and held my hand tight over the faucet tip. I did that a few seconds. I was glad to see water and sediment had shot out of the hot line into the bucket. I reattached the hot to the valve and opened the valve. Both hot and cold water flow were restored. So I haven't flushed out the cold line because I dont want to break what isnt broken. :)

My first guess is calcium or lime build up around the action, based on the quality of the water and the faucet. Hot water exacerbates build up of all minerals. Without knowing about your water or faucet, however, impossible to tell.

Any number of the single lever arc (non coil!) pull down faucets should do the trick. They have sprayers that pull down from the spout, and can cover the entirety of a sink. Most have buttons on the side of the faucet head, that provide a variety of sprays. I use the gentle berry spray on my Koehler Artifacts faucet, the most. I‘m quite familiar with the type of faucet/aerator combination your mother has. Back in the 70s and 80s, I had that, too. Believe me, these modern pull down faucets are a vast improvement. Here’s my sink and faucet. The Koehler Artifacts comes in two pull down sizes. I have the taller version. Click to enlarge. Google Koehler, Delta, Moen, Grohe...or just “pull down faucets”. Browse the sites, and see what appeals. When your state reopens from Covid-19 lockdown, perhaps go see the faucets in stores.