First, the Lord God issued this command to the man/Adam before Eve was created. Thus, Eve presumably heard the command from Adam. But, secondly, this does not necessarily mean that Eve misinterpreted what Adam said, or that she added to what Adam had told her. It is quite possible that Adam himself misinterpreted what the Lord God commanded. On this account, it means that what Eve says to the serpent is entirely accurate—she is faithfully reproducing what Adam had communicated. And it should be noted, thirdly, that the text of Genesis 2–3 itself doesn’t appear to condemn this one way or the other. If the narrative flow of Genesis 3 is taken seriously, then sin enters the world only once Eve and Adam have both eaten the forbidden fruit: ‘she took of its fruit and ate; . . . her husband . . . ate. Then . . .’ (Gen. 3:6-7, my emphasis)
It seems to me that the Genesis text doesn’t make any comment about the misstated command. But this suggests that mishearings, misinterpretations, differences of opinion, and so on, aren’t sinful in and of themselves. The problems arise when such misinterpretations go unchallenged (Adam’s passivity in Genesis 3:1-7, perhaps) and are given enough credence to mutate into disobedience and disorder. This is what happens in Genesis 3—but I don’t think it has anything to do with Eve’s embellishment of the Lord God’s command.