I found this photo online, perhaps it will help. In this picture the crown molding on the cabinets flow from the kitchen to the adjoining room. Maintaining continuity with the color and some of the trim detail will make the rooms transition nicely. Don't overlook the details like hardware finish, lighting and plumbing fixtures as these elements can also tie the two styles together. I hope this was helpful.

this room has one large window which takes up most of the wall facing north.quite a bright bedroom. would it look funny having a green, black and 2white walls? I just want to tie the black furniture in with a black fixture somehow. maybe you have other suggestion?

Textured linen or with a subtle print wont date. Feature walls make a room smaller as they jump out ar you. Wouldnt recommend. Get some interesting art or craft. Pick up colour with accesories

Personally , I wouldn't use that wallpaper -- it doesn't suit the apartment style IMO . I assume she wanted to add some focus and colour , but to me it doesn't work . To make it work ( or at least not 'jar' ) if she does insist on the wallpaper , pick out the burgundy or red of the wattle flower ( or whatever it is ) , and do a wall opposite it in that exact same shade , or maybe the kitchen area if you have good masking skills . The animal skin rugs look great , but the couch is 'lost' -- add cushions in the same red or burgundy as the wall , or go even brighter red or burgundy . Rest of the walls can be left as they are ( depending on wall condition ) or any similar neutral ( aka bland ) grey or cream , or possibly even a light steel blue .