A woman who smiled at detectives as she was arrested over the alleged bashing of an elderly woman in north-west Melbourne has been charged over the violent attack.

The victim, a 77-year-old woman, was discovered by a passer-by in Willaton Street, St Albans, about 7pm on Thursday.

Authorities said she was out walking her dogs when she was allegedly attacked.

Found lying in a pool of blood by neighbours, she was taken to hospital where she remains clinging to life.

9NEWS cameras captured a woman smiling at detectives as she was led away in handcuffs at about 10.30am yesterday.

The 30-year-old has since been charged with intentionally causing serious injury.

She will appear at Melbourne Magistrates Court later today.

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