VISA ON DIRECTIVE 2004/38/EC for family members of EU Citizens (Visa C)

Hello! I am Gabriel Foulc, I am a French EU citizen and I currently live and work in Antwerp, Belgium. I work as a filmmaker director of Photography and my partner, Alyssa Hope Bustamante is a Filipino national who resides in Cebu, Philippines. We were recommended to apply for the VISA ON DIRECTIVE 2004/38/EC for her to be able to join me here. We need some guidance and help to ensure a smooth move. One of our "main" issues is in the form of a proof of link, I am waiting for the answer of my lawyer if he can make an official cohabitation certificate with my partner, I've lived with her for 6 years, and the past 3 years we were renting the same apartment together where she lives in now. If the cohabitation certificate is not valid, my plans is to come back to the Philippines, and go on with the marriage process then apply. We want to know what is the best course of action and how you could possibly help us. Thank you.