Cannot resize objects (e.g. rectangles)

Alright, this is just stupid.....

Here's the problem:

My colleague and I are running identical versions of Illustrator (CC 2018, 22.1 in About), identical versions of OS X (10.13.6).

If I open a blank new file   I can draw a rectagle using the rectangle tool (M), and I can dynamically resize that rectangle using the selection tool (V) and the points on the rectangle (e.g. corners).

If my colleague attempts the same thing, she cannot dynamically resize that rectangle.  If she clicks on a point with the selection tool and tries to drag, she just drags the rectangle object around the screen.

You can't blame the file she's working on, because as I said, this happens with a blank new file.

Help ?!?!