tamtam, thanks for your kind words.
The vet put the needle in on her underside into the bulging area below her vent, but quite low down. Forgive my drawing!
The vet had to prick her several times to get anything out, even though it feels like a water balloon. She finally got yellow fluid...
tamtam84 - this thread has really helped me, thank you for sharing your experience, and the other contributors too.
I recently started a thread on a very similar thing https://www.backyardchickens.com/t/674230/ascites-and-internal-laying-sharing-my-experience-benedicts-story and have just read...