I suppose this is karma for me waking DSIS up when she was a baby...however I am now facing the same scenario. Dd2 is newborn (ish) and 4yo Dd1 wants to "check on her sister". I have asked and told her not to but she doesn't get it, or maybe she does!
Dd2 is not the best sleeper anyway and is now getting quite run down from it (sore throat/cold). I have much more success with getting dd2 to sleep when dd1 is not around (currently part time at pre school) but tomorrow is her last day until she starts school in a few weeks.
In the interim I need a plan (for my sanity and to help me stay patient with dd1). Dd2 mostly needs cuddling to sleep but this can take a while. Once she falls asleep we sit and I hold her for about 30 mins (or she wakes up) and then I put her in her Moses basket. Our downstairs is open plan and quite small so this all takes place right next to dd1. The alternative would be to take dd2 upstairs doing exactly the same but putting her in her crib - except so far she has refused to sleep in her crib during the day. I'm also not sure about leaving dd1 on her own downstairs for a potentially long period of time.
Am I facing the impossible? Do I just have to try and muddle through the next few weeks? Anyone been there, done that and got the t-shirt with any ideas?