What did she mean by that yesterday?

For the answer, let's look at Hillary's remark in the context of the campaign, the news of the day (Friday), the remark itself and Hillary's own frame of mind. In the end, I think I show that the objective of her remark was to tell her supporters to stand firm and help her gain the vice-presidential slot on the ticket.

The Campaign to Date:
* Marked by repeated references to race and gender bias, the campaign pits the first viable woman candidate against the first viable black candidate.
* The greatest danger of assassination accrues to the black male candidate, based partly on the historical record showing several instances of slain black leaders and partly on the fact that there is no statistical model capable of compensating for the scarcity of female candidates in past campaigns and thus, that might adjust for the absolute absence of any women slain in past campaigns.
* Recognizing the inherent danger of assassination, the Secret Service provided Sen. Obama with the first security detail for any candidate in this campaign, with the exception of Sen. Clinton, who has had one since becoming First Lady.
* Sen. Clinton has shown a determination to win the nomination that astounds even seasoned political observers. Her tenacity has become legendary.
* The current campaign season is the longest in many decades, by virtue of its extended primary calendar and because some candidates began campaigning more than 18 months ago.
* Exit polls record a marked unwillingness, largely on the part of Sen. Clinton's supporters, to support the opposing primary candidate in a general election.
* While there is some evidence of gender bias, particularly in the media, racial bias is evidenced even more by exit polling showing a distinct racial preference among up to 27 percent (WV) of white voters. The fact that black voters appear even more disposed to vote their race must be somewhat discounted in a year where African Americans are enjoying the first real possibility of electing a black president and because they have historically supported white candidates over black candidates in past primary cycles.
* Clinton has stressed her ability to lead by being "Ready on Day One."
* By Friday, Obama leads her in states won, the tally of popular votes in party-approved contests, pledged delegates and superdelegates.

The News of the Day (Friday morning):
* CNN reports high-level, formal talks between the Obama and Clinton campaigns over the possibility of Clinton as vice-presidential running mate (a story CNN later softened to talks among high-level, unofficial advisers of the two campaigns).
* Clinton superdelegate and California Senator Dianne Feinsten is among those openly advocating for a veep slot for a combined "Dream Ticket."
* Time magazine reports that former president Bill Clinton is driving the effort to secure a slot for his wife on the ticket.
* TPM posts a front-page story quoting chief Clinton fundraiser Hassan Nemazee as indicating anything less than a combined ticket may cost Obama financial and organizational support. He goes on to say: "It goes without saying that this argument is predicated on the fact that the single most important aspect of Senator Obama's decision is who is able to serve as president in a moment's notice should that need arise. And it is clear that Hillary Clinton fills that role."
* Edward Kennedy has been released from the hospital after tests reveal an inoperable brain tumor.
* One of Clinton's California superdelegate switches his support to Obama.
* A new poll in California shows Obama now leads Clinton.

The Remark:
* Friday, Clinton was interviewed by the Editorial Board (EB) of the Sioux Falls Argus Leader. Here is the relevant portion of the transcript, unedited:

CLINTON: This is the most important job in the world. It’s the toughest job in the world. You should be willing to campaign for every vote. You should be willing to debate anytime, anywhere. I think it’s an interesting juxtaposition where we find ourselves and you know, I have been willing to do all of that during the entire process and people have been trying to push me out of this ever since Iowa and I find it¬¬-
EB: Why? Why?
CLINTON: I don’t know I don’t know I find it curious because it is unprecedented in history. I don’t understand it and between my opponent and his camp and some in the media, there has been this urgency to end this and you know historically that makes no sense, so I find it a bit of a mystery.
EB: You don’t buy the party unity argument?
CLINTON: I don’t, because again, I’ve been around long enough. You know my husband did not wrap up the nomination in 1992 until he won the California primary somewhere around the middle of June
EB: June
CLINTON: We all remember Bobby Kennedy was assassinated in June in California. Um you know I just I don’t understand it. There’s lots of speculation about why it is.

Hillary's Frame of Mind:
* The interview takes place in mid-morning, when Clinton presumably is most alert and most rested from the grueling campaign.
* Clinton's support in California is eroding. Even Feinstein, one of her staunchest supporters there, is talking about a unity ticket rather than winning.
* A scant few contests remain, and they will not supply enough pledged delegates to overcome Obama's lead.
* Superdelegates continue trickling out for Obama, stretching his lead.
* She is being questioned about her reasons for staying in the race when hope appears lost.

CONCLUSION:
Was her remark less sinister than a threat but more substantive than a timeline reference? Was she arguing for a slot on the ticket because she could be "ready on Day One" and at "a moment's notice?" Was she making a veiled pitch to California supers to stick with her because "anything could happen" in the course of a campaign and only by being positioned in the number two slot could she count on an automatic promotion to nominee?

I think so. You decide.