In "Star Trek: Generations", Guinan is on the refugee ship, but in the "Time's Arrow" two-part episode, she is on Earth in the 19th century. The question is, how is it possible that Guinan was on that refugee ship, when she has already arrived on Earth? Didn't that refugee ship come directly from the Delta Quadrant after the Borg destroyed their world?
When we see Guinan in TNG: Time's Arrow, she's on a grand tour of the galaxy, listening to interesting species across the Delta and Alpha quadrants. It's clear from the original script that this is something her father isn't entirely keen on:
Guinan pulls Data past the partygoers and around a door.
GUINAN : Let me guess. My father sent you. Well, you tell him I've still got a lot more listening to do --
DATA -- I was not sent by your father.
After a few seconds of conversation, Data notes that she's not from his future but is, in fact in her correct timeline. He deduces that since her species is extremely long-lived and space-faring that running into her is merely a coincidence:
A beat; Data realizes that she doesn't know who he is, but decides he has no choice.
DATA : Circumstances demand that I take you into my confidence. I require your assistance. I am from the future.
Guinan reacts with surprise.
GUINAN : Is this some kind of a joke? No, you don't look like the joking type.
DATA: That is correct. I am from the twenty-fourth century, where you and I serve together on the same starship.
It seems likely that after having visited Earth, she subsequently returned to her homeworld. At some point in the next 470 years it was attacked by the Borg and her people made their way (by ship) to safety.
It's mere supposition, but Guinan may have played some part in the El-Aurian's decision-making process on where to go (e.g. "does anyone know somewhere that's friendly yet powerful and will give us unconditional asylum?").