Hillary Clinton does not have momentum. This is spin. She lost 12 primaries in a row before eking out a victory in the Texas primary and winning by a larger margin in Ohio.
However, in December, she was up by 30 points in Ohio and 20 in Texas. She lost both of those huge leads, beating Obama by 3 points in the Texas primary (and is currently losing by 12 points in the caucus) and won Ohio by 10 points.
She continues to trail in the popular vote, the number of pledged delegates, and the number of states won. Additionally, when all is said in done, she will have gained a net of 4 to 15 delegates only.
How squandering a 30 point lead is "momentum" is anyone's guess. Winning two states in which she was long considered the favorite is not momentum. Still remaining firmly in second place is not momentum. At the very best she slowed Obama's momentum.