Lindsay Lohan is mentally prepared to move on with her life … because she finally completed her court-ordered psychotherapy sessions … TMZ has learned.

Lohan had been ordered to complete 18 sessions as part of her sentence in the jewelry theft case … and we’re told her last session finished up yesterday afternoon.

Sources connected with Lindsay tell us … the actress feels therapy has “made an impact” on her life … and she’s learned different techniques to help her handle difficult situations in the future.

Lohan is due back in court tomorrow … we’re told she’s hoping Judge Sautner will continue to be impressed with her progress … and not sidetracked with that whole maybe, maybe-not hit-n-run fiasco.