Most people are questing WHO fathered Reyna but in my opinion thats not important but rather WHY?
I believe Myrrah took human sperm and impregnated herself and the sole purpose of Reyna was a back up plan. Myrrah knew if she died and without her human intellect the war was lost so she planned to raise Reyna with her the same values she has. I believe Reyna was born after E-Day. Myrrah did not intend to love Reyna as a normal mother would but I believe she did end up loving Reyna and sheltered her from the war and not teaching her to hate humanity and Reyna loved Myrrah shown by her necklace that she values alot. During operation hollowstorm Myrrah had to leave Reyna or maybe lost her during evac but regardless I believe she was saved by a young COG gear and the two would eventually birth Kait. Tell me what you think and feel free to add to it or poke holes in it. Theirs more details but this is the general theory.