Okay, back to business... but without being able to actually *see* how you are sailing in the "overpowering" conditions that lead to the problem.
Some gear issues/things that can lead to that unpleasant "lifting" sensation... are boom too high for you (probably best at shoulder to chest height), harness lines set too far forward, harness lines a bit too long which means that you can't really commit to the lines and harness, perhaps not enough downhaul on the sail which can put too much power in the upper part of the sail where it is hard to control, especially for we women who do not have the upper body strength of the guys who thus have a better chance at control.
If your boom is at a good height, check your harness lines. Most people when learning, have them set forward, and long, in order to practice getting in and out of them. However, once you are really using them, the lines should be moved back a bit (try 5 hands or so from the boom attachment) and the lines shortened. This is because as you pick up speed, you'll be moving back on the board, sheeting in more, AND beginning to rake the mast back. If you don't begin to lean the mast back as you sheet in and move back, the center of effort of the sail will be too far forward and it will try to lift you off the board. If you *simply* move the mast back without having the speed, you'll just steer upwind, so there is some attention to technique involved.
Again, I haven't seen you sail, so I may easily be telling you things you already know and are doing, so please understand.
One important thing that you don't want to have happen, is to let your shoulders get pulled in front of your hips because then you have only arm strength to work with, and that is a losing battle. If standing up, your shoulders are directly over your hips, you have "neutral" leverage; if your shoulders are in front of your hips, you have no leverage and only arm strength; but if your shoulders are behind your hips and you are not bent at the waist, now you have lots of leverage and lots of leg strength (your largest muscle group is the thigh group). When your shoulders are behind your hips, you'll want to lean back against it as though it were the power boat pulling a waterskier, and the pressure should be through the front of your feet and not the heels. No pressure on the heels, as though there were a tack, point side up, in the heel of your booties. One can survive some major gusts by leaning out with the shoulders and straightening the legs.
If you then sail into a lull, you'll have to roll your shoulders in over your feet, and sheet out a bit to save yourself.
It is tough to type windsurfing instruction since it is such a dynamic sport, and there are so many variables, but I hope something here helps a bit. Please let us know how it goes.