James crossed the line in the 71st minute to seal a 20-17 victory over Merched Clwb Rygbi Cymry Caerdydd.
She said afterwards: “The girls have taken me in as part of the family, I’ve never been more proud of every single person that’s here.
“That try was for the team. It was absolutely surreal, it was only a few weeks ago I was here watching Wales play England. It was amazing.”
She added, “I’m grateful for every person who has come down here and supported us through thick and thin. They knew we could get here and we’ve done it.”
Haverfordwest Ladies captain Emma Summons echoed her teammate, describing the experience as “class”.
“I’m so proud of the girls. The first half we made a few mistakes but when the crunch came, we bottled down,” Summons said.
“Thank you to every single person who has supported us along the way. It was great to see so many people make the journey down.”