it sucks, but it is not your call. you will never know why she got promoted...could be she did som ething on a project you were unaware of, or has more time in grade, or maybe she slept with someone. not worth the time spent thinking about it. different companies have different reasons & guidelines. even in places like the federal gov't promotions are never cut & dry even tho they should be. don't waste your time & energy fretting over thinking your skills are better then hers so you should have earned that slot. for what ever reason, you didn't..so don't go down that rabbit hole. worry about your skills, your position only. sounds harsh but really it is what only matters. anything else will lead to trouble. don't ask management why she got promoted..it is not their reason to give..beyond a "she was better suited for the position"

the company may or may not be well run..sometimes what seems to be one thing from one level is totally different from another. that's where employees get in trouble at times...thin king above their level. you can't begin to know what goes into management decisions...it is a whole different world up there. speaking as someone who worked both entry level & upper management in one company. little fish, big fish. policies are totally different when explained from both levels. best advice...do you stuff..leave the management advice to them.