If you are very depressed and so low you cant function, can you admit yourself into hospital?

On a mental health ward? Im asking on behalf of a friend whom im very concerned about. I myself have been on a mental health ward for afew days respite when I was about 21years of age through depression and anxiety(bad eating disorders leading to self harm etc) or does she have to have someone section her? Please can anyone with genuine knowledge answer this question? Thannks so much. M. She would go into hospital, but cirstances and family relationships/commitments means she doesnt want to burden them, long story......... so I just leave you with the ? and hope someone can give true answer.