>they are unable to see the Shipping Address field.
that is correct, because the shipping (aka delivery) address should really be added to the checkout form in the first place
or the plugin will never have any information about where to send the order to . And as that is typically the case, asking for the shipping address again once in the paypal payment screen is superfluous.

that said, if you want to enable this anyway for some reason or another , you can do this by using a filter like so (not tested, but should work just fine)

add_filter('wppizza_filter_paypal_parameters', 'myprefix_set_paypal_parameters');
function myprefix_set_paypal_parameters($parameters){

	unset($parameters['no_shipping']);
	/*
		or instead try one of the below if the above does not work
	*/
	//$parameters['no_shipping'] = 0;
	//$parameters['no_shipping'] = false;

return 	$parameters;
}

note: this applies when using the paypal standard redirect implementation (which you are seemingly using)