As I recall our son received an LOA in late October of last year (for the class of 2014), received his nominations in November and received an appoitment offer in late December. He first noticed his online USAFA application status changed to "appointment offered" before we actually received the appointment in the mail (BFE - big fat envelope) so keep watching for a status change to her online application.
This all happened fairly quickly for us, but I don't know that this is necessarily the case for everyone. My hunch is that the LOA appointment offers probably go out first, but I don't know this for a fact. It just seems logical that they try to resolve the status of their LOA candidates first.