Rewrite the sentence in Active voice. Her birthday is being celebrated by her.

Then identify the tense of the sentence and in the active form use the same tense.The given sentence is in the present tense because helping verb in the passive form has “is being”. So the active voice will be in the present continuos  tense, The verb in the passive form is the past participle of the verb. celebrated is the past particple of the verb celebrate. By is used before the object/doer of the action. Here “Her birthday” is the subject and Her is the object so they are interchanged. So the verb in active voice will be “is celebrating” .