From the delightful Dear Professor Einstein: Albert Einstein’s Letters to and from Children comes the following exchange between Einstein and a bright, witty South African girl named Tyfanny, who reminded Einstein of his own granddaughter and with whom he exchanged several letters despite being at the height of his career and cultural prominence.
In a letter dated September 19, 1946, Tyfanny writes:
I forgot to tell you, in my last letter, that I was a girl. I mean I am a girl. I have always regretted this a great deal, but by now I have become more or less resigned to the fact. Anyway, I hate dresses and dances and all the kind of rot girls usually like. I much prefer horses and riding. Long ago, before I wanted to become a scientist, I wanted to be a jockey and ride horses in races. But that was ages ago, now. I hope you will not think any the less of me for being a girl!
Sometime between September and October 1946 — a snappy response time by the day’s standards — Einstein replies:
I do not mind that you are a girl, but the main thing is that you yourself do not mind. There is no reason for it.
Source: Brain Pickings - Women in Science: Einstein’s Advice to a Little Girl Who Wants to Be a Scientist