You can edit the template file to use the replace function to remove part of the label.
in the webassist/email/templates folder, open the template that was created for the email..
the code to write the label will look like:
<?php echo(str_replace("_"," ",$pkey)); ?>
change it to:
<?php echo(str_replace("_"," ",str_replace("Appointment_request_group_","",$pkey0)); ?>