When motion verbs 行く(go), 来る(come), and かえる(return) are used in the Vている pattern, they express continuance of the state created by the action(i.e., a person has gone/come/returned somewhere and is still there).
兄は タイに 行って います。
My older brother has gone to Thailand. = My older brother is in Thailand now.
マナさんは 日本に 来て います。
Mana came to Japan and is still here. = Mana is in Japan now.
ジョンさんは 国に かえって います。
John has gone back to his country. = John is back in his home country now.
Lesson 11-4「マリアさんは てがみを かいて います。」
Maria is writing a letter.