I do not know if Abdu'l-Baha ever sent a valentine to any of the women in his life. (He had a sister, a wife and four daughters.) If he ever wanted to send a valentine, he might well have considered sending the message found below.
"The handmaids of God must rise to such a station that they will, by themselves and unaided, comprehend these inner meanings, and be able to expound at full lenght every single word; a station where, out of the truth of their inmost hearts, a spring of wisdom will well up, and jet forth even as a fountain that leapeth from its own original source. "
The above quote was taken from Tablets of Abdu'l-Baha Abbas, vol. 2, pg. 473.