Bicycle Mechanics - wobbly cogset

I was helping a friend get her Huffy cleaned and sort of rideable.
While I was cleaning the chain I noticed that the cogset wobbled like an out of true wheel. I looked at the wheel, and while it's not perfect, its not terrible. Does she have a problem with the axle or is it more likely to be a problem with the freehub?

Cluster "float" is common. (Since the axle does not rotate, it is not the culprit.) Grab onto the cogset and check for excess play. One can reduce play in an old-fashioned freewheel by loosening the retaining ring (CLOCKWISE), removing one of the shims, and retighening the ring (anticlockwise). If your friend is very unlucky, the freewheel may be cross-threaded on the hub, which would cause pronounced freewheel wobble, even in the absence of bearing play.

Yup. I second everything John E said. You just noticed the float for the first time. It is very common.

yup. if its a freewheel then float is very common. dont worry about it.

Is float normal for 9-speed Shimano cassettes, too? I've noticed when my bike is on the stand and the rear wheel is spinning that my cassette wobbles. It shifts fine, and I'm not experiencing abnormal wear, so I haven't done anything to it.