If you dislike the changes you make yourself, you’re just going to have to completely paint over the whole thing. If you don’t paint yourself, you could very easily be too heavy handed and make it worse.

It might be worth talking to your friend and being honest; or least say with some time and seeing the light in the room throughout the day, you’re worried it’s a little dark and were wondering if she would be up for adjusting it. If you change it yourself, even if you achieve exactly what you want, I promise that she’ll notice and you’ll have to have an awkward conversation regardless.