sounds like she is trying the controilled crying method although i would have thought that looking in on the little chap was part of this! is your sister easy to talk to? It can be a very sensitive issue so it can, telling another woman how to raise their child although you mean well and only have your nephew's best interests at heart i would proceed with caution. she actually may think that she is doing the very best thing. Try talking about how you managed with your children when they were unsettled in the night,and how hard you found it (no parent finds it easy do they) she may feel she is the only one who has ever struggled and may find it hard to express that in words without feeling a failure. she may open up to you especially as you say she is your younger sibling.Do you live with her? maybe you could offer to help her out by getting up to check on him, she may be relieved! does she have a partner? what does he think? I hope things go well for you.