"Displayed appreciation", "expressed thanks", "conveyed gratefulness", "revealed indebtedness", "demonstrated recognition", "manifested thankfulness", "demonstrated acknowledgment", "exhibited thanksgiving", "proclaimed recognition", "rendered thanks", "voiced recognition", "uttered gratefulness", "acknowledged with gratitude", "appreciated with gratitude", "recognized with gratitude", "thanked with sincerity", "gratefully acknowledged", "generously thanked", "gratefully appreciated", "earnestly recognized". These are some synonyms for the phrase "showed gratitude" which can help one to express their appreciation and thankfulness to someone who has been kind and helpful.