Sam Bates' secret to her best ever WBBL season at the Sydney Thunder was convincing herself her career was almost certainly over.

Bates will enter Wednesday night's knockout final against Hobart at Drummoyne as one of the Thunder's key weapons and leading wicket-taker with her left-arm finger spin.

The 32-year-old will also do so with a fresh two-year deal in her pocket, ensuring the Thunder's most-capped player will be around until 2026.

But for most of the past year, Bates believed her career was about to be finished.

After an underwhelming 2023-24 season where she was cut by Victoria and took only five WBBL wickets, Bates moved back to Newcastle ready to finish her paramedics degree.

She began training with NSW in the pre-season, but even when she was called up to play for the Breakers in September she still believed this summer could be her last.

"It put life in perspective," Bates told AAP.

"I actually decided early on, if this was my last season of cricket, that was going to be OK.

"It took a huge weight off my shoulders, not putting any pressure on me to try and be someone different or bowl something I am not good at.

"If I was going to not have a contract it would suck, but I would still be OK.

"I think that's what's also put a real big clarity on where I was going to bowl and led to good bowling performances."

Bates' 2023-24 summer was impacted by injury, and she came into last year's WBBL underdone after a foot issue.

But she is also the first to admit concerns over her future had impacted her cricket.

"There was definitely a mental drain last year," Bates said.

"What I came up with I was just putting so much pressure on myself to be someone I wasn't, to be a cricketer that I wasn't.

"I was able to work with Lisa Sthalekar a little bit in the pre-season this year to work out who I was and what I wanted to bowl. And I just wanted to own that."

Bates has absolutely done so.

She claimed four-wicket hauls in two separate matches this year, while her 19 scalps at an average of 12.1 make her the WBBL's second-leading wicket-taker.

Her form had helped the Thunder sit first on the ladder with one round to play, but they now face the task of needing to win three straight games to clinch the title after a last-start loss to the Melbourne Renegades.

They do at least carry a home-ground advantage at Drummoyne into Wednesday's knockout with the Hurricanes, with the winner to go to Brisbane for a grand-final qualifier against the Heat.

"It's mixed feelings," Bates said.

"We haven't hit out straps yet, we haven't played our best game yet going into finals when it is a do-or-die situation."