Sergio one thing I can tell you is we women are very complicated, intense, serious, emotional and at times hysterical beings. With that being said...all in all it means, we experience 'feelings' different from guys. From something as simple as a first kiss...the woman is already seeing a future with this man whereas the man is wondering if the kiss is possibly going to lead to 'other' events.
We 'hear' more in the conversation than men do in general and that's why we tend to over analyze the heck out of life in general.
2 women can get into an argument and that's it...friendship over...2 dudes...might not speak for a day or week but can promise you that if it's anything less than sleeping with the others lady...they can easily work it out and mend fences.
Women harbor a LOT of baggage because of our sensititivy and my guess...and that is all it is, is that she has probably had her heart broken badly in the past.
Maybe she enjoyed the pace in which things were flowing prior to the love letter.
I do think she owes you an explanation, but whether you want to hear what the explanation is is entirely up to you.
Give her some time, don't blow her phone up with constant calls, don't bombard her email...a simple email or text or message asking simply...'what did I say to make you leave'...should suffice.
If you don't hear back from her...then maybe later down the road, a couple of weeks...email, text, leave her a message and tell her how you feel that she has handled this. Don't curse her out...but remind her that you have feelings also and she has hurt you deeply. Let her know that you thought her to be a much better person than she has displayed and lastly let her know that you will never try to contact her again.
Sometimes when we women get that 'final' word we panic and we start to wonder and ask ourselves did we make the right decision. After that give it some time...if she reaches out to you...take it from there. If she doesn't...let your heart mend before moving forward.
Best to you Sergio....