I find it really sad that some parents are so obssessed with their kids rooms being 'tasteful' and insisiting on neutral walls. Why? Why does it matter if their walls are white or pink?
We have always allowed kids input.
We have had flower power curtains with pink and turquoise walls.
Jungle animal curtains with lime green walls
Purple curtains and duvet with yellow walls
New York skyline duvet with beige walls and black curtains
etc etc
They had their room choice aged about 3/4 and then again aged about 9/10 and then again at about 13.
I was careful to make sure it wasn't too much of a whim, and that it looked nice and co-ordinated when done, and they didn't get to redo it until the next roudn came, so they had to live with it for 4/5 years.
It is like character duvets which some parents will not allow under any circumstances. Why? Who really cares what is printed on the duvet cover?
My kids adored their Hot Wheels, Thomas the Tank engine, Jungle, Dr Who etc etc duvets.
I get curtains from ebay (new, £20 for black out lined decent curtains) and then it is just the cost of the paint.
The now unwanted duvets (well-used for 5-10 years) either get passed on to happy younger kids, sent to charity, or used as spares when their friends visit, which causes great hilarity.
Honestly, I do find it strange that you wouldn't allow your kid some choice as to their own space.
For the OP, I would tone down the pink on the walls, just because it will be a bit overwhelming, but buy bubble pink duvet and curtains and as someone suggested a large fluffy rug.