Britney's little sister is slated to field ground balls and take hacks at the plate at the University of Louisiana Monroe ... in an effort to help the school's softball team raise funds.

It'll all go down at 6:30 PM -- and general admission tickets start at $40 ... but for an extra $20, university officials say you can get an autograph from her following the game.

Jamie said in a statement she signed on for the event in part because of her daughter, Maddie, who's an up-and-coming star in the sport.

"I'm raising a young female athlete," she said, "so I'm honored to be asked to participate in an event to raise money for other female athletes."

The "Zoey 101" star -- who's most recently been in "Sweet Magnolias" -- told Extra Inning Softball she's taking things pretty seriously ... training with Maddie so she can impress at the dish.

Maddie's a pretty good coach for JLS to learn from ... take a look at one of her home runs that Jamie Lynn recently posted -- she's got a swing!