Clinical depression results from a chemical imbalance in the brain, which causes mood swings, lethargy, feelings of self-loathing, and general bad behavioue. Reactive depresion is, as the name suggests, caused by a traumatic event, either recent, or subconciously revived from the past - the symptoms are the same.
Both respond to medication and counselling, the recovery times vary depending on the individual, and the severity of the condition. The first step is the sufferer realising they need help, and receiving medication and / or counselling as deemed appropriate by their doctor.
You need to be patient with your colleague - a major symptom of depression is a severse sense of worthlessness and self-loathing, which often makes the sufferer try to make others dislike them as much as they are disliking themselves. It is involuntary, and it is part of the condition, so please advise anyone who is in contact with this lady about the situation, and hopefully she will recover in time.