I've got a few questions. First, what and when is "women's day"? Second, you country says "USA", but you said "behaviour". This sticks out like a sore thumb to anyone who actually is from the USA. I also fail to see how her losing her virginity to you, relates to her being rude or cold towards you. I suppose those things don't matter too much in and of themselves, but I am curious. Anyway, on to business. You should respond to the letter in a positive manner if you actually care about her and want to continue to put up with her coldness. If you are fine dealing with her behavior then continue to do so. If not then you need to move on.
...one can be sure of nothing until it has already happened...