Sorry none of our ladies have stepped up to answer your question here.
I had a similar problem many years ago, but it was not from an injury ,
not from climbing on the board, and not from waterstarting.
My hands and wrists would burn and cramp after any several hour sailing session
The pain (after sailing) was noticeable and one of my sailing friends was an intern MD
at the local hospital.
She suggested that since I have quite small hands that the larger (1.25"/3.175 cm) diameter booms and big sails (7.5-9.5 m2) I was using were putting too much stress on my hands and wrists.
Her suggestion, after seeing me wringing my hands and wrists at post sailing pizza dinners, was to get smaller diameter (1.125"/2.8575 cm) booms.
Also she suggested fairly heavy doses of anti-inflammatory drugs (3 200 mg Advils) after
Use of the smaller dia. booms, and occasional Advil binges (after many hours of sailing or racing) have kept me sailing pretty much pain free for around 20 years.
Also, I concentrate on not "gripping" the boom.
I learned this from the coach of the USA Juniors Formula Experience Team where some of the girls on the team were having wrist issues.
Teaching them to "play the piano" on the top of their boom with all the fingers while sailing or racing on 8.5 m2 FE rigs, keeps your grip on the boom much more loose.
You hold the boom fine, but you do not "grip it" tightly which causes lots of hand and wrist stress.
Also use of an Easy Uphaul device on larger sails, and having your harness lines adjusted to take as much load as possible off your hands and arms and put those loads down on the much larger muscle groups in your hips and thighs are good strategies for reducing hand and arm stress when windsurfing.
Hope this helps,