Horrible! I know seasickness too well, and also get very travel sick in cars.
To add to all the other good advice - in particular spend time afloat but not necessarily out there in big waves to begin with - if you are really ill then:
(i) lie down, preferably in the warm and dry below. Take a bucket with you. Sleep (you will, honest). You will feel better after and this is much better than being cold, wet, in the way and miserable in the allegedly fresher environment
of the cockpit
(ii) drink hot water
. This really helps me. Cold water
makes my poor stomach feel worse, and any flavouring etc has predictable consequences. But hot water will stay down, comfort me and combat dehydration.
(iii) hold on to the fact that it will pass. Honest. It may take days but it will pass and (whatever you hope for) it won't kill you.
If you are both worried she will be really incapacitated then start slow and small and possibly with friends. Don't set off for a long, offshore passage
before either you can manage without her for (say) 24 hours or she's over the worst.
We use stugeron and ginger. Also a drug called Buccastem in the UK which is an anti-nausea drug. It will knock you out but after the one dose you'll be much better able to cope.