it can simply be " gửi mẹ" or " thưa mẹ" or like the lady commented above.

Besides the way two ladies show you above, you can use " Kính gửi mẹ" (to show your respect ) . or "gửi mẹ yêu" ( to show your love)

It depends on how you are close to your mom, maybe " mẹ yêu dấu... " or " mẹ thương mến... ",.....