As far as i'm aware the boss' only really need to a couple of hours to change the shifts for casuals (i could be wrong). Where i work (will not name) we are struggling to keep our profit and loss down so we have to cut shifts...for example when i started more than a year ago on a saturday we had a good 5/6 people on all day... now we can only afford two people all day and and two people half day...and generally the cheaper(younger) staff get the hours...again to save money...i dunno if there is anything you can really do? maybe ask if she can go part time? i think it's a minimum of 13 odd hours and they will be guaranteed (same times same days etc) and can work up to like 32hours? dunno if this helps but just thought i'd give my two cents

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1997 White GC8 WRX - 3" TBE, Apexi pod, V6 STI TMIC, Kei Office coilovers, Whiteline F strut brace, GReddy Profec B Spec II, 2004 F&R brakes..