E.G.
Hmmm. I'd suggest putting the youngest to bed half-an-hour earlier than the oldest. My kids have separate rooms, but the half hour after tucking in my 3-yr-old is high quality time with my 8-yr-old. This is the time he tells me all the happiness and sorrows of his life. Sometimes we just snuggle and read. If your daughter is really high-energy, perhaps the two of you could take a walk. Then big sister can "tip-toe" to bed like a big girl, so as not to wake her little sister. I also play the same lullaby CD every night... without fail. The repetition helps lul them to sleep.
E. G