Ours have been sharing a room since DD stopped sleeping in the co-sleeper, at maybe 2.5-3 months old. I think only time will get your DD to stop seeing it as playtime. Mine do fine, although DD doesn't sleep throught the night yet (never has, still up 2-3 times a night). DS usually just sleeps right through her waking up. Sorry not much help. But it does work :)
Thanks! I think I just needed some encouragement to stick with it!