Well, this is awkward. Susan is well aware that she knows things about Rukia that the shinigami wouldn't normally tell people. It's in her nature to be forthright, however, and while she's wary of revealing things that might be in her future, she feels she ought to come clean about the rest.

"I should mention," she adds in a low voice, pitched for Rukia's ears only, "I ... know a few things about where you're from. And who you are. You -- the future you --" or the alternate Rukia, but let's not get into that now, "-- had to tell me that, because you'd gotten involved in some matters close to me. But you may count on my discretion here."