The Email copy of shipment
checkbox can be disabled from configuration.
Looking in the template that renders that section you will see this:
<?php if ($this->canSendShipmentEmail()): ?>
<p>
<label class="normal" for="send_email"><?php echo Mage::helper('sales')->__('Email Copy of Shipment') ?></label>
<input id="send_email" name="shipment[send_email]" value="1" type="checkbox" />
</p>
<?php endif; ?>
This means that the checkbox is shown only if $this->canSendShipmentEmail()
evaluates to true
.
Going deeper on this you will see that the config path sales_email/shipment/enabled
determines if it's allowed or not.
The value for that config path can be changed from System->Configuration->Sales Emails->Shipment->Enabled
.
Set that to Yes
and you will see the checkbox in your other website.