Since the device uses a motor and the motor gets hot, it sounds like it is pulling a fair amount of current. Many smart plugs are not designed for motor loads. The Zen25 that you were using specifically says not to use it with motors.
One switch that does work with motors up to 1/2 HP is the Zen15. I have one on my washing machine to alert when the load is finished. I have another on my backup sump pump to monitor when it operates, which is rarely.
You might be able to put a temperature sensor on the motor casing to alert your wife when the motor starts to get hot and then shut off the power when it is too hot.
The ZEN15 is a Z-wave device. There are some Zigbee plugs available, but I like the ZEN15 as it has power monitoring, which might be useful for your application. Make sure you get a plug rated for motors as some have a high startup current. Get one rated for 15 amps or higher. The ZEN25 was only rated for 10 amps resistive load, so it would not work well with your motor.