Only another 160 odd posts to go pompom and then you'll be done with the same repeat posts 
My dd is nearly 16 now and I think the 12-14/15 years can be tricky (I've clearly blanked my own teen angst from memory - much like childbirth). In many ways I think I almost had to revert to toddler thinking when parenting during early teens.
So for example, my dd would go through periods during her early teens when she was constantly hungry and consequently hangry. But it took me a while to connect her bad moods with need for food.
Similarly, they are in an in-between world - not children, but not proper teenagers - so they may find the "young/teen girls" clothes in some shops too "young" but don't yet fit into the adult ranges in Top Shop etc.
They are pushing for freedoms but at the same time are actually wanting boundaries to be reinforced so they have security.
And don't get me started on the nature of girls friendships during this period and the comical (in hindsight) nature of her frustrated attempts to leave home and walk to her friends house when she was grounded.
I don't say all of this to give you a parenting lesson, but just that as I was caught in the eye of the early teen storm I often forgot the whirlwind that was constantly enveloping her and I'd end up fighting ridiculous battles when I would have been much better served stepping back and guiding her out of the storm.
If it is any consolation, at nearly 16 we seem to be more or less out of the whirlwind. So as you already know this isn't about a bed or a bedroom really, it could have been about dying her hair green or staying out till 1am on Wednesday night because "Donna is always allowed to do that.."
I would also agree with a poster up thread that teenagers today are really living in a different world with pressures coming in a way unimaginable when I was young. For all the benefits there are to being a teenager in 2018 Britain (or elsewhere) am not sure I would swap places with my DD.
(sorry for the essay!)