The back of the card has an intriguing message.
The message sent to Marinda Locke in 1923 reads:
We start on our homeward trip tomorrow and by Friday afternoon I shall be telephoning to know how you and our professor are. My love to you both and to your dear brave mother. K.L.B.
I found some information in the Mount Holyoke College archives that may help to explain this message: Marinda Adams Locke graduated from Mount Holyoke College in 1893. She worked at various schools before becoming a nurse in 1898. Thereafter she worked at a hospital in Boston, Massachusetts. It sounds as if she never married.
Her sister Adelaide Locke also graduated from Mount Holyoke (1892) - and from the Hartford Theological Seminary (1896). She taught Biblical History at Wellesley, and according to the book In Adamless Eden: The Community of Women Faculty at Wellesley by Patricia Ann Palmieri, she lived with her mother.
So, why does the message refer to the 'dear brave mother'? Well, it seems that her daughter the professor was probably in ill health, since she died the following year. Presumably Marinda was there to help with nursing duties. Marinda lived until 1951.