The Torah obligates us to vocally recall the punishment Miriam received for speaking lashon-hara about Moshe. There were numerous factors that might have mitigated the gravity of Miriam sin and thus her punishment:
(1) She spoke about her brother whom she loved dearly
(2). She risked her life to save Moshe when he was an infant.
(3) She raised him in his childhood
(4) She did not say anything actually derogatory about Moshe; she merely minimize the extent of his greatness.
(5) Since she did not speak in Moshe’s presence, he didn’t suffer embarrassment.
(6) She did not speak against him in public; she privately spoke to Aaron, her brother.
(7) Moshe I was the paragon of melody and was not affected by what Miriam said about him.
Nevertheless despite her righteousness Miriam was punished with leprosy. Anyone who speaks Lashon-Hara/Evil Speech violates the commandment recall what G-d did to Miriam.