I don't even have a photo of this one, but I saw it last Tuesday....

Daisies, like plain white daisies with yellow centers, blooming on a bush.
Foliage was in whorls, not like daisy leaves at all.
It was 6' high.

What the heck is it???

If we can't find it this way, I'll drive back out there with my camera.

My first thought was Montauk Daisy (Nipponanthemum nipponicum) but it's supposed to stay about 3' tall so 6' would be unusual.
Here's a link anyway: Montauk Daisy (Nipponanthemum nipponicum)
There are some good images of the foliage so you can see if there are any similarities. I'm guessing you saw this in Pittsburgh?

Actually, I think that is it!
Yes, I saw it on the outskirts of Pittsburgh.
I'm 5'3" and I was eye to eye with the top of it.
In Spring, I'm going to ask for a cutting....

I cannot find reference to it ever being over 3' tall either.
Maybe the one I saw was some cultivar.....