He wouldn't be wrong there. Billie may be curious enough to ask but she isn't invested in what may or may not be upsetting Jonathan Strange. Mostly, she just ends up shrugging at his regret about dying.

"Well, it's just shit luck that you did," she says to that, which probably isn't the kindest way to offer comfort for this. "But what's the point to regretting it? You'll just mire yourself in the past and let it drag you down."

Of course, for all that she would claim she has no regrets herself, she sure sounds bitter about something there for a second.