Assalaamu alaykum. I do not know whether you have received my email, but if you did, then I would like to apologise for this inconvenience. I asked if it was an act of Shirk (associating partners with Allah) to talk to people with pagan names, and from what I undersood from the answer, it is not, but what if a Muslim was to talk to a person with a name that was Shirk and the person was an atheist and of the opposite sex? Could this be an act of Shirk or disbelief? What if the Muslim was trying to call that person to Allah?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

What you mentioned, that the addressed person is an atheist and her name is indicative of Shirk, does not affect the permissibility of talking to her and calling her with her name. This is not considered assertion of Shirk; it is merely an assertion of the name she is known by, and this is permissible.

Ibn Al-Qayyim wrote, "The statement of the Prophet, sallallaahu ‘alayhi wa sallam, 'I am the son of ʻAbd Al-Muttalib,' was not intended to approve the use of this name; rather, he was simply mentioning the name by which that person (his grandfather) was known. Informing people of a name to identify the person spoken about is not prohibited. The issue of informing is of a broader scope than the issue of giving a name." [Tuhfat Al-Wadood]

Allah knows best.