I understand that she worked hard to create the space she wanted on her side and why she may be disappointed that your side is not coordinated and therefore the room's two halves are not cohesive.
Sure, it is offensive to be told your side is boring, but I honestly do not think she tried to hurt your feelings but maybe she just wanted to motivate you to put in a little more effort.
You need not copy cat what she has. But, there are ways to spruce up your side without spending a lot of money because it sounds like you just need some creativity.
I say this just to keep the peace, as you are stuck with her for an entire school year.
Step back and take an objective look at your side. Is there a way you can make it more tidy? Or perhaps pick a couple of colors and stick with that color pallet? Shopping at thrift stores can net you tons of great things at fabulous prices. And, remember, spray paint is your friend. There are so many spray paint varieties available today that you can transform anything with a can of spray paint.
You need not spend a lot of money on bedding. maybe find a cheerful comforter, a bookcase or a night stand that has storage capabilities. I bought a hanging wicker-type plug in overhead lamp. It was ugly and stained, but it had a great shape, so I spray painted it and now it is a showpiece for $7.99, plus $3. for paint.
At the same time, you must be yourself and not feel like you have to clone your side to match hers.
But, making a little effort may be good for yourself because that is where you sleep and probably study, so it should be your happy place.
Or, do nothing but keep your side tidy and clean if you are totally happy with it.