It draws Bellatrix back into reality, that is for sure. She has helped herself to a chocolate filled croissant and a particularly fascinating bit of scripture from his library, courtesy of waking before he did and needing something to do that hasn't directly involved terrifying his grandson or the more questionable domesticity of peacefully lying next to him while he slept.

"Just sugar, please." That she requires ridiculous amount of that go without saying. "And I would like to kindly remind you that you only bought this one because I let you have it."

Making a scene at McKinnon's would just be inappropriate. Besides, inviting herself to Lucius' library is never regrettable.