Emmara, Soul of the Accord

• WWizards of the Coast2018-10-05
  Official Ruling
  For the ability to trigger, Emmara has to actually change from untapped to tapped. If an effect attempts to tap Emmara, but it was already tapped at the time, this ability won't trigger.
• WWizards of the Coast2018-10-05
  Official Ruling
  Emmara's ability is a triggered ability, not an activated ability. It doesn't allow you to tap Emmara whenever you want; rather, you need some other way of tapping it, such as by attacking.

Rulings via Scryfall