Snapping to a vertex doesn't seem to work for me. The pivot point is set to median point, and I have enabled scaling under snapping options. I don't understand why blender doesn't scale the shape to exactly the size of the circle I've selected.
Note that the "circle" I am trying to scale is not a perfect circle, since I messed it up previously due to the mirror modifier. However, also note that this ellipse was previously scaled down from the circle I'm trying to snap to, which is why I'm trying to scale it back to its original size.