When its blowing hard or getting gusty fly the kite low and close to the water, and edge deep with the board. With practice you can plough upwind and stay in control in really rough water and overpowered gusts. Your harness can feel like its going to be pulled down your legs! The kite will also be forced closer to the side edge of the wind window, and this can help with control.
If you fly the kite high in overpowered conditions you will be lifted up, loose your edge, and loose control, lofted, and your board may be left behind. So keep the kite low.
Be carefull how much you depower the kite. If you depower it too much it may not fly smooth and you will loose control. Its better to fly it lower and edge harder with less de-power.
Also, if you have a big board try sliding your feet back towards the heal edge to help edging, even if at first it feels looser. I quickly swapped from a 138 to a 123 board when beginning and found it way easier, though many people dont and it has other disadvantages. So a smaller board might or might not help you too.
Fly the kite lower, edge harder, keep practicing, and you will master the gusts.