Has the client had a history of ankle sprains? Any bone fractures? Ligament damage? What is the ROM at the ankle, knee, and hip? Any low back issues as well?
I start clients off with a foundation movements at all the joints. One, to see the ROM. And two, proprioception is often diminished in chronic injury/instability. Moving the joints through the ROM helps stimulate the PNS.
So for the ankles, dorsiflex/plantarflex/invert/evert/circumduction cw/ccw. All of those can be progressed with resistance slowly over time.
Without more info and actually seeing the client, I would be hesitant to suggest more.