Imo it IS Felix and Felicia's baby. That woman looking for her baby is actually the "good part" of Felicia. In one of the chapters where Diha Sion talks with 5 elders or something like that, he talks about finding something-something-i-forgot-the-name to make Felicia complete.
Also in the chapter with nuclear explosion where Felicia supposedly dies, Diha seals her madra, not the whole Felicia. That's why i think that "evil Felicia" is just her madra or some part of her.
Thought the same thing here.