Hillary Clinton is replacing the person (Patty Solis Doyle) who was the campaign manager for both her senatorial campaigns as well as, until now, her presidential race. Replacing Doyle is Margaret "Maggie" Williams, a longtime close personal friend and confidant of Hillary Clinton.
A typical campaign structure sees the campaign manager supervising the daily operations, the tone and messages the campaign sends, while the candidate concentrates on her public appearances. It requires a mix of management skills unlike and in either the public or private sectors. You can tell a lot about how well a president will govern by how skillfully she or he chooses the campaign staff.
From my research, Margaret Williams is a highly successful manager with experience in business, foundation, and political staff management. As far as I can tell, she has never run a political campaign in her life. While this may be the biggest operation she has ever managed, I suspect Williams will be excellent at managing the mechanics of the campaign, the ebbs and flows of money and staff. However, she has no experience managing the ambiance of a campaign.
This suggests to me that Hillary Clinton is taking upon herself the duel role of candidate and her own campaign manager. This is dangerous for a campaign. A campaign needs people who are emotionally detached steering it. As Bill Clinton proved in South Carolina, you cannot allow a campaign to become clouded by anger, fear, pride, or excess exuberance.
Williams also brings heavy baggage to a general election campaign. She was Chief-of-Staff to Hillary Clinton when she was First Lady and was an assistant on Bill Clinton's White House staff. In that position she was involved in one of the lesser scandals of the time, the Johnny Chung case. Arianna Huffington today remembered those times.
Anyhow, to answer the question I posed above, the staff shake-up is a sign of reasoned panic. The reasoned part is, if the campaign continues along its current path she shall lose the nomination. Something had to be done to change the path. The panic part is leaning excessively upon people whose most prominent qualification is personal friendship. It is a sign of paranoia, of distrust in the staff you hired.