1995 Chevy Cavalier Tire worn on one side, vibration at mos

I drove about 850 miles this weekend, and above 65 the car would vibrate a lot, with the steering wheel shaking.

After the drive up (400 miles), I took it to Walmart to have the wheels balanced. When I came back, they said the order had been cancelled with "unsafe environment". They later explained that it was because the tires were "cupping", which indicates a problem with the suspension, so they didn't do the balance.

Since then, it seems to be vibrating even worse. I can feel it at 35 MPH.

The front right tire is worn in one spot, which is obviously because of some kind of balance or suspension problem, but I don't think it matches the descriptions of "cupping" I see online. It's only worn on one "side". I don't mean it's worn on one edge and not in the middle. I mean the pattern of wear is only visible with the tire rotated in a certain position. In other positions the tread looks pretty normal all the way across.

Does this seem more like an unbalanced tire/wheel, alignment, or failing suspension problem?