Now add in the problem of her species being slaughtered by the Borg yet they've managed to make it so far into Federation space circa 23rd century when their domain was much smaller
There's no reason to think the Borg domain was smaller in the 23rd century. The Waadwaur (mistakenly?) thought it might have been smaller in the 16th century, but even if it was, this may merely have meant it was centered around the El-Aurians and Earth back then.
and yet no El Aurian saved discussed anything about what happened to them
Nicely in keeping with how Guinan clamshells throughout TNG, nicht wahr?
(nobody on the Enterprise-B was curious over what the ships were, what happened, and so on?)
One of the ships was named Robert Fox. I don't think there was any mystery over what the ships were - they were merely the last link in the chain that took these refugees to Federation space. But the skippers of those ships probably would have had little idea of where their self-loading cargo was coming from, there having been so many links before that.
And the refugees were refugees exactly because they had not seen the Borg. Otherwise, they would have been Drones. So their testimonies probably wouldn't have amounted to much anyway.
I see no problem with that part of the story. The audience knows going into the theater who the Borg are. The heroes of the main story know that, too. That the heroes of the prologue do not is just a great bit of extra fun.
Timo Saloniemi