its true they are inconsistent, but I will have a go at examining how it may have gone down.
OW at first kept quiet and proclaimed Allison's public persona, happy, content etc....... I mean why air dirty laundry? but days later, as the severity of the situation becomes frighteningly apparent, she is now considering the next possibility (in her eyes) and feels compelled to share a little bit more as it really has become an actual concern for her. She has probably been told by GBC that there was a big fight (supposedly) she has probably been told Allison was extremely upset. She has probably done what I think a lot of us would do at this initial stage and said....'relax, she is fine, she is probably cooling off, calming down, she wouldnt do anything stupid. etc etc'
she may wholeheartedly believe Allison has packed up and pissed off and needs a few days alone. (IMO this happens even with little kids, although often the mother takes them too, but we don't know the situation at that particular time)
It quickly becomes apparent that this isnt likely maybe due to Olivia being given more info about recent events, and she becomes quite worried for Allison, and also how things are looking for her brother now.
So as I write this I am starting to believe it!!!!!! In fact, your comments that Olivia's "statements were in actual fact those of an innocent, ignorant's woman's resonate with me. She may too have been anxious because she had doubts about her own family as you suggested