Went out on this beautiful vessel while on our honeymoon.
http://www.windwardschooner.com/Wife fed the fish the whole way out to the Tobago Cays. Even getting in the water to snorkel didn't help (which usually cures it).
She is perfectly fine on my parents powerboat (in the background) and our dinghy, even when choppy on the Chesapeake.

She also gets sick if too far below deck on a cruise.
I never have and never will understand it. I have not been in the Navy, but I was raised around boats my whole life and have been on all types of vessels, in all types of weather and have never been seasick. It is a shame too, because we would love get a cruising sailboat, something big enough to take to blue water, but we haven't found a way to keep my wife from being sick...