iss actually just took over from ess for servicing the rio tinto sites in the pilbara. the website is below
http://www.au.issworld.com/Pages/default.aspx
As mentioned spotless do a lot of the site maintenance for rio tinto so they would be good to contact. Site below.
http://www.spotless.com.au/
Of course she could look at the rio, woodside and bhp websites but most of the cleaning and maintenance jobs go to contractors. A big one for Rio is Skilled (
http://www.skilled.com.au/) They do a lot of the semi-professional jobs.
I know most of the big companies up here are deperate for workers, so good luck to her.