Firstly extend WC_Email class to define the email header, subject, email template for content
secondly, add custom email class to the default WooCommerce email classes using woocommerce_email_classes filter, with trigger that calls terms
if ( has_term( 'Your Cat', 'product_cat', $item['product_id'] ) )
lastly, Create an email template to be used to generate email content for your custom email.
this answer to this question involves a lot of code, far too much for SO so you may want to do some reading like.
https://cloudredux.com/adding-sending-custom-woocommerce-email/