Tigers, the league leaders, have lost only three games all year, but two of those were in finals to Rhinos, who again handled the occasion better than their near-neighbours.
Castleford looked to be on track to a big win when they led 8-0 after six minutes, through tries by Maisie Lumb and Lacey Owen, but Abby Eatock’s brilliant solo conversion halved the gap at half-time.
Cas’ kept Rhinos’ Woman of Steel Courtney Hill quiet in the first 40, but she grew in influence after the break, setting up an equalising score for Fran Goldthorp.
The 16-year-old doubled up with a brilliant solo try soon afterwards and Hill’s conversion opened a six-point gap.
Hill then sent Elle Frain over for a touchdown which she again converted and Kelsey Gentles’ late touchdown was little more than consolation for Castleford.
“The first 10 minutes, they stuck to what we asked them to do,” reflected Castleford’s coach Lindsay Anfield.
“Fatigue set in a little bit and they just reverted back to type and started doing their own thing, which is really disappointing.
“Leeds do the basics really well and I have no complaints.”
Leeds’ Adam Cuthbertson was delighted with the never-say-die spirit shown by his team.
“There’s so much character from the girls,” he observed..
“They’ve got this unbelievable ability to never give up. That shone through in that second half when we started kicking to the corners and defending our line really well.
“I’m so glad for them, they’ve worked so hard for this and deserve every bit of it.”
Castleford Tigers: Stanley, Lumb, Eastwood, Owen, Gentles, Roche, Cudjoe, Field, Peach, Hoyle, Dodd, Renouf, Marshall. Subs Watts, Lumley, Townend, Slowe.
Leeds Rhinos: Beevers, Nuttall, Eatock, Kerrigan, Goldthorp, Butcher, Hill, Anderson, Gaines, Johnson, Staveley, Booth, Webster. Subs Bennett, Frain, Priim, Oldroyd.
Referee: G Dolan (Batley).