I swear it's only open like 3 hours a day...anybody else notice this?

Do you fast travel a lot? Fast travel can offset the merchant hours I've heard.

I rarely fast travel. This is the only shop that I had do this as well. I'll check the wiki

NPC schedules in general do not do well when you fast travel or use the carriages.

I almost never fast travel or use the carriages and I've noticed the same thing on three different playthroughs. That lady is almost never there, I've waited outside her shop sometimes for 7-8 hours, one hour at a time, and she never shows up. When I get really far along in a game I will fast travel more sometimes, but I never notice any ill effects on merchant schedules, the proprietors always maintain their normal hours. I noticed it again just recently because I was trying to become thane in Dawnstar and there don't seem to be many favor quests you can do there, the alchemist in town has one (which I've done before) and I was waiting for her to open her shop so I could talk to her and get the quest. Waited from just before noon until after dark and it was another no-show.

Edit: UESP says she sleeps above the store, opens around 8 AM, closes around 8 PM, and then spends 4 hours at the local inn before going home to bed. I can tell you that in my last 3-4 games, that store has never been open from 8-8 any time I've been in Dawnstar and tried to go there.

I didn't know there was an alchemy shop in Dawnstar.

In my experience, there might as well not be one.

I haven't been to said alchemy shop, but I also haven't noticed any impact on merchant hours from fast traveling.

Some people just like their skooma and tree sap too much