Finally...I kept seeing this thread title and pretty much ignored it until I kept seeing it stay active and posts kept piling up. Perhaps I would have clicked earlier if the title stated "passenger" buffetting. Anyway, if you folks don't mind a little hillbilly engineer speculation, perhaps it will at least humor and distract during our current "Hunker Down Virus" situation.
In one of my (too many) careers, I sold paint spray booths. Not just for your neighborhood body shop, but all types for industrial manufacturing. By necessity, It taught me a good bit about AIRFLOW. Think of airflow as equal to current. Even a lazy lowland river has current. Buffetting equals turbulence. (white water) So...what we are seeking to do is stabilize the airflow and reduce the turbulence. The solution will not be exactly at the windshield, but the area where the air current meets that tiny wisp of a little lady sitting behind you. (Lucky you)So, it is not just the height of the windshield, but the angle, and you too...your size, and perhaps riding position.
So...your challenge is to find the combination of elements that promotes smooth air current to her space and if turbulence occurs...have it happen behind her. A predictable stream of airflow can be a pleasant experience. Turbulence is unsettling... like being slapped around. Don't merely think about how tall the windscreen is, but pay a lot of attention to the angle and especially...width. I don't have the exact magic answer in my shirt pocket, but hopefully, you will be able to find the combination that extends your airflow past your sweet companion and leave the turbulence to flutter and dissipate in your bike's wake.
Back to spray booths and airflow. I learned that air loves to flow in a straight line. I can give you a great quality of clean filtered air if we can control the entry and exit of the air in a predictable linear flowing manner. But introduce obstacles, twist & turns, and the resulting turbulence/buffeting (little tornados) will pick up trash, & debris that would have otherwise not taken flight.
If you find an acceptable solution, come back and let us know. We can all benefit from such experiences. All the best to you and your mate.