You can include the module ActionView::Helpers::TextHelper
http://api.rubyonrails.org/classes/ActionView/Helpers/TextHelper.html#method-i-simple_format
class Request < ActiveRecord::Base
include ActionView::Helpers::TextHelper
after_create :attempt_send
# ...
:html => "#{simple_format(self.body})"
--
Another option which doesn't include all of the TextHelper methods, just the one(s) you need is to use delegate.
delegate :simple_format, to: 'ActionController::Base.helpers'