She is going to make a new dress change into passive voice

"A new dress is going to be made by her" is the passive voice

Explanation:

A sentence can be written in two voices: "Active Voice and Passive Voice". When a sentence is written in active voice, it emphasizes on the "subject" of the sentence, i. e. one who is doing the action. In case sentence is written in passive voice, the action (or the verb) is emphasized rather than the subject. A sentence is mostly written in active voice.

In the given sentence, "She is going to make a new dress", the stress is on the subject 'She'. To change the sentence to passive voice, emphasis is made on the action of the verb, i. e: "A new dress is going to be made".