Isn't it obvious in exchange for winning the war she gets to eat Saru for dinner. After all winning a war is a lot of work and she deserves a treat! My real guess is all she really wants is to secure her freedom when everything is over( in other words not live the rest of her life under guard) so she's willing to help but the war has to won her way and Starfleet doesn't seem to have a lot of options at this time.