Is the wife sinful because her husband uses the computer for forbidden things, whether the device was hers previously or she gave it up?

The device became yours after your husband gifted it to you, and it is not permissible for you to enable him to use it in what is forbidden, except under duress that is considered valid, in accordance with the Almighty’s saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." Similarly, it is not permissible for you to gift it back to him if you know he will use it for what is forbidden. Now that the device has returned to your husband, you must seek forgiveness and repent, and advise him on the obligation to repent from viewing what displeases Allah.