Ibn Kathir commenting on the meaning of the mention of Maryam bint Imran, as “يأُخْتَ هَـرُونَ” (O sister of Harun) :

(O sister of Harun!) referring to the brother of Musa, because she was of his descendants. This is similar to the saying, `O brother of Tamim,’ to one who is from the Tamimi tribe, and `O brother of Mudar,’ to one who is from the Mudari tribe.

It has also been said that she was related to a righteous man among them whose name was Harun and she was comparable to him in her abstinence and worship (contained in the Qur’an sura Maryam (19) verse 28, source)