My daughter doesn't want to wear nappy at night either since the second daughter was born 2 months ago. Similarly, she says she's not a "baby", it's her little sister that's a baby. But we talked firmly with her and told her that she will wear it until for 1 full week there's no wee in the nappy. So now when she wakes up, the first thing she does is remove her nappy, throw it in the bin and wear her pantie (she's toilet trained for the day) so that we won't "discover" anything!