my manager and my co-worker are best friends is it appropriate?

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i work at a gas station with nothing but women, (not saying anything is wrong with that) but my co-worker whos a sales associate, and my manager is best friends, they hang out together and go out to bars, that isnt the problem tho, ive noticed how my co-worker always gets catered to when it comes to duties which need to be performed around the work place, to nobody having weekends off but her, me and other fellow employees also noticed this and one acctually confronted her, only to get brushed off...what do you think should be the next thing to do?