Like many a confessional Lutheran, I do not follow the modern rule of abandoning the historic liturgy in favor of some mother's day theme every time the second Sunday in May rolls around. It's Eastertide, after all, and there are more important things to preach than matters which make Hallmarks happy.
Having said that, however, I am by no means averse to the honoring of our mothers on Mother's Day. On the contrary, I believe that he who dishonors his mother dishonors God who gave us all our mothers.
Therefore I have consistently followed the practice of including a special Mother's Day prayer in the General Prayer (i.e., the Prayer of the Church). Anyone who needs a prayer for Mother's Day, feel free to use it if you like. Only don't make it a collect for the day; just include it among the petitions:
O Almighty God, who didst send forth Thy Son to be born of a woman, the Blessed Virgin Mary, and who by His holy incarnation didst in truth cause her to be the very Mother of God, thereby crowning and honoring all motherhood, grant Thy perpetual favor and blessing upon all of our mothers, that they in turn may be a blessing to all their children. Bless the memory of those of our mothers who have passed on from this vale of tears, and leave us not comfortless. Grant also to the Holy Christian Church, which is the Mother of us all, prosperity in faithfulness, that we through her pure milk of the Word may gain everlasting joy, through the Son of Mary, Thine only Son Jesus Christ, our Lord.