A lovely Bible verse that you could include in your mother's birthday message is Proverbs 31:25-26 (NIV):
"She is clothed with strength and dignity; she can laugh at the days to come. She speaks with wisdom, and faithful instruction is on her tongue."
This verse beautifully captures the qualities of a strong and loving mother, making it a heartfelt addition to your birthday wishes. You might add a personal note expressing your love and gratitude for all she does. Happy birthday to your mother!