Video tape her playing a set/serving/volleying/drilling.
For me, it did not really 'click' in my head on some things until I could actually see what people were telling me. Especially on my serve and on my positioning at the net...I *felt* like I was doing what my pros were telling me, and when I finally saw that I most definitely was NOT doing what I thought I was, well, it was eye opening and much easier to work on and improve.
Though, I still get threatened to be whacked in the butt if said butt is not close enough to the net!
The latest thing my pro is working with me on specifically for doubles is 'chipping and charging.' Chipping the return, then get to net. Again, I *thought* I was chipping (and not swinging at returns) until one lesson when the light bulb went off! Personally, I *hate* it!!! I want to swing! Slowly but surely I'm getting better at it (I think!). High levels doubles is played and won at the net.
Fast volley drills at net have also helped my develop faster 'hands' at net as well. It used to be that I would hit a good volley, not expect it to come back, and then be caught off guard when it did. I still get caught, but sometimes I'm doing the catching as well!