*Spoiler*
It just made no sense her waiting this long to suddenly call in her favor to Fred to help find Filip. She had plenty of political capital to spend after Eros. Just hard to imagine her suddenly becoming so motherly that she wants to find Filip now. I can see the counterargument that he's grown up without her and probably has had his mind poisoned against her, but it still didn't make sense.
I think the affect of her being so close to the belter family in Ilus may have changed her ... and it seems there is stuff we do not know or have not heard yet, or even forgotten. Something about how she got the change to remake her life ... I am not sure I know what that was about, but it was responsible for her hanging out and living low? I can't remember now, back the opening of the first episodes.
Or, she had a breather finally, and now realized she had a way to find her son, whereas before she was really out of the loop.
You're right, they did try to provide some buildup, especially with her speech to Lucia. But still, she told Holden about her son back in Season 3, I think, and she made it sound like he was permanently lost to her. If all it takes to find him is a phone call to Fred, then that should have happened long ago.
Then again, you may be right that she was so traumatized by the loss she couldn't pursue him, she just had blocked out the possibility of finding him as a sort of self-defense. But I'm still having trouble digesting it.
I think she was either a fugitive, or not on good terms with Fred, or maybe she did not realize that Fred and Marco Inares were antagonists? That did not bother me so much.
She had said that Marco got her involved in something bad and she got blamed for it, but that she had the chance to remake her life. I am not sure what happened to Naomi ... so her story will unfold in Season 5.
I hope it is not too long a wait.