"Ella exige la liberación inmediata."

She demands immediate liberation.

duolingo limited the translation to the difinitive answer only, but the others are equally correct. It's just that demanding an 'immediate release' is usually how the phrase is said, not that it is the only way of saying it.

She demands her immediate release. Why is "her" incorrect?

Wow! Talk about a feminist! You go girl!

she demands liberation immediately..........