* Disclaimer - Jaycel went through this process 6 months ago, so things may have changed *
That being said, nowhere at any point in the interview process did the embassy ask for a welcome letter from Jaycel. They only asked her Appointment Confirmation print-out, DS-160 confirmation page, passport, NBI Clearance, Birth Certificate, CENOMAR, the sealed medical exam report from SLEC and the passport sized photos.
The Manila Embassy has a reputation for being hit or miss in sending out the welcome letter - That's why K-1 Visa applicants don't wait for it.