defintiely ask and email beforehand! you want your LOR writers to have a heads up that it's coming their way. I sent all 3 of mine an email at the beginning of july last year telling them when OTCAS opened, and when they would receive a notification about writing it. I also thanked them again for writing it, and for my professor, i included a bit of info about why I asked them to write the email, and how their classes were specifically relevant to me going to OT school. especially if you havent already asked them to write it, definitely make sure they are ok with writing a letter of rec, and include why you feel they are the best person to write it!
