"I gave her back her computer."

Translation: Je lui ai rendu son ordinateur.

[Sky_Larme]

why not je l'ai rendue

[Sitesurf]

Because this is an indirect object: rendre quelque chose à quelqu'un:

Je lui (to him/her) ai rendu

[lavenders_pink]

not fully understanding this, could someone explain a bit more why 'je l'ai rendue son ordinatuer' is not the correct answer?

[Sitesurf]

There is an indirect object: rendre quelque chose à quelqu’un ». The pronoun should be « lui » (= à+il/elle).

[LynnMoelle]

Seems like this could also mean "I gave him back his computer". Is this one of those situational situations?

[Sitesurf]

Since "lui" is the indirect pronoun for "il" and "elle" when the preposition is "à", you are right, "je lui ai rendu son ordinateur" can be translated to your masculine version as well.

When you get the French sentence for back-translation to English, you will, therefore, have a choice between the feminine and masculine versions.

[CSA_GW]

Can we say "redonner" as "give back" please?

[Sitesurf]

You can now.