It is a different word because it is not the word for grace.Mary's "full of grace" announced by the angel is from her beginning " that is where the belief in the Immaculate Conception is indicated. Stephen's "full of grace" was "at that moment" and can't be compared to the Blessed Mother's.
I have been told that the greek word 'kecharitomene' is not used in Stephens reference but some kind of variation of 'charitoo' and would relate to a certain point in time.
The following was copied from Catholic Answers as posted by 'Jimmy':
Luke 1:28 reads:
kai eiselqwn proV authn eipen, caire, kecaritwmenh, o kurioV meta sou.
The word kecaritwmenh is used here. This is a perfect passive participle. It is also feminine. A participle is a verb that is used to describe the subject. The perfect tense describes an action in present time which has a completed aspect. In this verse it is used as a title and means basically "you who have been graced" or "you who have been filled with grace". This word is not speaking of just a little grace, it is speaking of an abundance of grace. Although this is a completed action, the effects are still on going in this verse. Mary is still full of grace when the angel says this.
I already showed you how other translations translate it.
It does not translate "full of grace" because there is no "grace" in the expression. Why not try translating the word properly instead of relying on RCC propaganda.Perhaps your understanding is wrong.
Luke 1:28 And the angel came in to her, and said, Hail, thou favoured one! the Lord is with thee: blessed art *thou* amongst women. (Darby--very literal)
Luke 1:28 And he came in unto her, and said, Hail, thou that art highly favored, the Lord is with thee. (ASV)
Luke 1:28 Having come in, the angel said to her, "Rejoice, you highly favored one! The Lord is with you. Blessed are you among women!" (WEB)
Luke 1:28 And the messenger having come in unto her, said, `Hail, favoured one, the Lord is with thee; blessed art thou among women;' (Young's Literal)
One translation after another does not support your opinion.