YANBU, OP. She's old enough to be sure about this, and it sounds like you've given her more than just a slap of paint, this is a whole new room.
Also, to other posters, I got DP a coffee maker for his birthday. Yes, it's a kitchen appliance, but it's hardly an essential one. I mean, we need the microwave (for sterilising at least), we neeed the oven and the fridge, but the cofee maker is a luxury item, because if you can't afford one you can still have coffee. If you don't have a kettle you can only biol water on the hob in a pan. FWIW, my mum got an expensive oven as a christmas prezzie too. To all those not in ivory towers, the more expensive appliances (as in, not the cheapest oven/fridge/microwave but a high end one) are luxuries just as much as a new telly or fancy car would be.
As it happens, DP loves cooking, so ideal gifts for him in thepast have been Le Creuset cookware and good quality knives. Likewise, for a girl who has a history of trashing furnitue (as the OP said midway through the thread) an entirely new and redecorated room would indeed be a gift, and backing down now and getting her extra could cause problems where she expects this treatmwnt again.
Not everyone has the money to just redecorate willy nilly. In the entire time I lived with my parents, my room was never redecorated purely for my benefit or to my taste. (My mum did magnolia everything when she decided to move but this just meant I was never allowed to personalise it after that and basically lived in a guest room all through my teens.) At my dad's house our room still had a nursery border on the wall from the people who lived there before he did. I was 20 when I moved out and he's only just redecorated. To me, having a room decorated how I wanted would still be an amazing birthday and/or Christmas present.