Did she? We got that information second hand from Ezra, a lawyer. That was why I said that not everyone seems to be telling the truth. We don't know what she actually told Ezra, we only know what he told Miriam.
The point I was making was this. (And yes, there's supposition here but I'm looking for the "minimum lying" case.) Put yourself in Jacqui's position in early '89. You find out you're pregnant. You come back to the happy home we probably got a glimpse of in 255. And there are Pat and Miel rejoicing because - guess what - Miel is pregnant. And - oh yeah - sorry we might need your room.
You give that nice Ezra a ring - hoping for one in return (just supposin'). You meet up in a diner (because 23 years later Ezra is going to find himself in a similar and related situation and it will make a neat call back). What do you tell Ezra?
"My guy's wife / other girlfriend is pregnant too. I don't want to tell them I am."
"I'm pregnant and he doesn't want to know."
? ? ? ?
421 tells us Jacqui didn't tell Pat and Miel, doesn't it? Why would she tell Ezra the truth? Either Jacqui lied to Ezra in '89 or Ezra lied to Miriam in 419. I know which I think is more likely. (But it is only that: more likely.)
We have absolutely no evidence that Ezra knows who the father is. If he did, he
might have picked up on who Adrian is without having to be told. As I've said, my take on the conversation between Jacqui and Ezra in 418 is that Miriam is going to want to know who the father is and Ezra isn't going to be able to tell her: he can't tell her the full story; Jacqui will have to.
As far as we know, despite their little chat, Miriam still doesn't know she's Adrian's half-sister. Jacqui apparently recognizes that she needs to be told that. As I see it, she thoughtfully allowed Ezra to break the news to Miriam that he's not her father. But that was all he was able to tell her.
EDIT: Just to add
However, the exchange over the phone between Jacqui, Pat, and Miel also seems to partially contradict what Jacqui told Erin when she confessed who Pearl's father was. Does that mean she didn't have the fantasy, had the fantasy but never told Pat the truth, or didn't fully spell things out before she disappeared with Ezra? Or something else?
The "I probably should have run that idea by them first" line in 398 only need mean "before I got pregnant (at the same time as Miel)"; it doesn't have to mean "before I told them I was pregnant".
(And Jacqui does confirm in 393 that Ezra doesn't know who the father is.)