Would it be a sin to return the wine, which the delivery driver left at my place in her absence, to my unbelieving neighbor?

It is forbidden to sell, buy, gift, carry, or store alcohol, based on the Almighty's saying: ﴿O you who have believed, indeed intoxicants, gambling, [sacrificing to] stone altars, and divining arrows are but defilement from the work of Satan, so avoid it that you may be successful.﴾ (Al-Ma'idah/90), and because the Messenger of Allah, peace and blessings be upon him, cursed ten categories of people related to alcohol. Therefore, if the gift is alcohol and this is known from the outset, it is not permissible to accept or keep it. However, if it was not known upon receipt and it later became apparent that it contained alcohol, then the delivery person or the maid must be contacted to take it back immediately. There is no blame if you received it as a trust and did not know it was alcohol, and carrying it with the intention of disposing of it is permissible.