Guidelines for conversations

Is it correct for one member to make another member who hasn't attended church in a long time (for confidential and good reasons) to feel somehow inadequate or sinful by saying to them: "I know you don't care," when in fact the opposite is true?

Your question contains a context of which I am unaware. If someone has upset you with unkind or unfair words, you want to speak the truth in love to that person (Ephesians 4:15). If someone has sinned against you, rebuke is in order (Matthew 18:15; Luke 17:3).

When it comes to the actions of other people, the Bible instructs us not to judge hearts or motives (Matthew 7:1).

“The God of peace be with you all” (Romans 15:33).