The contract is associated to the mobile number. My understanding is Optus won't allow a mobile number change only a name change.
Technically I guess it's something that's possible although there's no set in stone process. Once the transfer has gone through, we'd need to cease your existing account with us. Do you remember if the mobile number originally came from Optus or had you ported the number in from another provider such as Telstra ect? If it's the former then your number would be placed into a quarantine, we can pull this number out of quarantine and perform a number change on your daughter's service.
If the number originated from another provider, the number would be sent back to the donor carrier and you'd need to complete the reactivation process through them. You'd then need to port that number back to Optus on a prepaid mobile service (it's a bit of a headache to deal with).