The answer to your question is "cry-it-out in the crib and sleep through the night".
Big sister will do fine, she's heard her cry and can tune the crying out. Don't be afraid your children will hear sounds when they're sleeping, they NEED to learn to block them out and sleep. Experts recommend you keep family sounds the same when you bring a newborn home, within reason of course, so they can adjust to you, not the other way around.
If you haven't already establish a bedtime routine that relaxes her and prepares her for sleep, quieting things down a bit and dimming lights. A bath, a rubdown with nighttime lotion, pj's and fresh diaper, a quiet song or short story as you nurse her, encouraging her to nurse fully, not snack. She should be at the point she gets all her nutrition through the day so she can sleep through the night and if you're feeding her a good meal she's not hungry when she cries, it's habit and not knowing self-soothing techniques. Keep the lights low and talk in soft whispers to set the mood for sleeping.
Lay her down groggy but awake, she needs to learn to self soothe. Keep a soft nightlight on if it's pitch black in her room, and to see by if you need to change her. Pat her a minute or so as you gently say "Good night, I love you." Then quietly leave and close the door. If she cries do not go in for at least 10 minutes, leaving the light off, speaking in a whispered "time to go to sleep" and leaving her in her bed, don't pick her up. Lay her down, pat her a few seconds and leave. If she cries again wait 15 minutes this time, adding 5 minutes between going to her each time. No more talking, walk in, no lights, lay her down, pat her or lightly rub her back or tummy until she's calm and leave. If you get to the point she needs a diaper change do it in her bed, don't take her out, no lights, no talking, just matter of fact, a few pats and leave. Your not giving in to her crying to get up consistently will teach her bed = sleeping. It may take a few nights or longer, much longer if you give in as she'll know she can win if she keeps crying, but if you stick to this she'll get it and you'll have her out of your bed :)
_______________________________________________
Just saw this and thought I'd share:
http://shine.yahoo.com/parenting/8216-crying-8217-favor-k...