you are using the helper to render a translation also:

        - if user_can_send?
          .send_kiito
            %p= t 'kiitos.user_dashboard.history.can_send'


the 'can_send?' helper returns a string because is being used as translation scope, so if you reuse it you can have something like:

.send_kiito
  %p= t(can_send?, scope: 'kiitos.user_dashboard.index.instructions.history')

and just add another key to the en.yml file:
...
history:
  form-enabled: 'my cool text'