User blog comment:Night at the Kashmir/My Theory why Sally was really sent to Fontaine's./@comment-1500935-20140923224508/@comment-24769282-20140926024139

As for the Big Daddy, it could be very well possible that given a certain amount of time together that Sally and that Big Daddy were able to form at least the Type A bond that Solarmech mentioned. Though I believe that the Big Daddy had already been there regardless if Sally was there or not, because as far as I can tell, the Big Daddies were still maintenance workers before being bonded which was sometime after the war. If that Big Daddy were to be a test subject, as Pauolo said, Suchong would never allow that.

Given the unused line, it could be that either that Big Daddy was just continuing his maintenance despite it's obstructions and then became unstable with Fontaine's or thanks to the retractable drill, went mad and travelled to Fontaine's by its own accord.

I believe that Sally was not necessarily bonded with the Big Daddy at all. This is evident in the fact that when Booker and Elizabeth arrive at the Housewares Department, we see Sally being harrassed by a splicer but not a Big Daddy in sight. It's only when they arrive in the Toys store, of which was barricaded off with a warning "he's in there", that Sally's yelling attracted the attention of the brute. So my theory is that that Big Daddy was just territorial, like the Toys department was his domain. Though my theory could be defunct due to why he ended up in the Bathysphere DeLuxe walking amongst splicers.