The sister of gangland widow Roberta Williams is set to fight charges she stole $35,000 in luggage from Melbourne Airport carousels, and claims she has been unfairly treated by police.

Police allege Michelle Kaye Mercieca repeatedly stole luggage from the airport between October 2017 and September last year, when she was arrested by police who had CCTV footage of a woman grabbing bags from a carousel at Tullamarine.

Michelle Mercieca says she's been mistreated by police. Credit:Luis Enrique Ascui

Police later found seven suitcases at her Kings Park home.

Ms Mercieca, 51, who faces 19 charges of theft, fronted Broadmeadows Magistrates Court on Tuesday, when her case was adjourned to a contest mention next month.