- She lost the delegate derby
- She essentially tied Obama in the popular vote
- She lost more states
- She lost the January cash war (and the cash war since, see this below, plus Obama is up to 7 million (Hillary is at 4M) but Obama's amount does not include fundraising that MoveOn is doing for Obama, which should be released later today.)
- The calendar is her enemy
To see why these facts could cause her concern check out the piece. It's not too long, but informative.