Answer:
The packet shall be mailed to her (by me).
Step-by-step explanation:
In an active voice, the subject acts upon the verb meaning the subject comes before the verb. But the passive voice reverses that, making the verb act upon the subject.
In the given sentence, the subject is "I" and the verb is "mail", and "the packet" is the direct object. So, using the concept of the passive voice, the object will come first, followed by the verb, and then the subject.
Thus, the final sentence will be
The packet shall be mailed to her (by me).