In my current FO3 playthrough I got Sydney as a permanent companion without even trying.
I was on the Stealing Independence quest, and proceeded through the National Archives without encountering Sydney (not on purpose, I just didn’t run into her).
I made it to the Button Bot and agreed to help forge a copy of the Declaration (so the quest was not completed).
On my way out of the National Archives, I encountered Sydney for the first time, and agreed to help her.
Then I left the National Archives and Sydney followed me. She’s been my companion ever since. I usually tell her to wait outside my Megaton residence because the outer reaches of the Wasteland are a bit too dangerous for her. When I went through Raven Rock, which normally fires all your companions, it did not fire Sydney.
This is on an Xbox 360, I’m wondering if anyone can confirm this behavior on their platform and maybe it could be added to Wikia (I did not see it there).
To be clear, I haven’t finished the Stealing Independence quest and probably never will since I’d rather have Sydney as a companion.
Have never heard of this glitch, but it accidentally fixes a serious error. The game really should have left open the option of recruiting Sydney after Stealing Independence is completed.
For those on PC there is a mod that makes Sydney a companion. It includes a bunch of additional dialogue recorded by original voice actor Karen Carbone specifically for the mod, which is pretty damned cool. Some of the new dialogue is quest or geography specific. A great mod: Sydney Follower.
Original Link – Continuation of discussion