It's true that Babs couldn't have known any of that. That's why she's being thoughtless and inconsiderate: it just doesn't occur to her that someone might be hurt or offended by hearing her toast someone's death, no matter how evil that someone might have been. On top of which, there's nothing "apologetic" about Barbara's "overtures of friendship." After Helena has clearly indicated that she is, in fact, offended, Barbara never apologizes at all. She defends her actions, then insists she's not naive, then changes the subject. At no time does she do anything to acknowledge that she might have given offense.
Moreover, while "bitchiness" is, I suppose, in the eye of the beholder, Helena is certainly not being confrontational. She's the one who says "Nevermind. I have no right to judge you." It's Barbara who behaves confrontationally, insisting not only on not letting things go, but also on psychoanalyzing this complete stranger she has just met. That's pretty obnoxious.