First I would warn you to be very careful not to compare the two or expect either one of them to do somehting just because the other is. They are completely different people and personalities even they they were born together. The last thing you want to do is give your daughter a "why can't you be more like your sister" or " but your sister can do it" complex. I am a younger sister and trust me that will follow her throughout her entie life!! If she's not interested - then don't worry about it. She's obvisouly seeing her sister doing it and I'm sure she knows and understands "how" to do it if she wans to. Children learn in different ways and in different times. For many of them, the more you push, the more they resist and vice versa. I spent a few days showing my daughter what to do - she knew how - but didn't really want to, especially if I wanted her to. So I just left her alone, told her that she didn't have to and went about our lives. A few months later, she woke up one morning, asked to put underwear on and has been potty trained ever since. In the mean-time, try to find other things that you can praise her about and be proud of her for. They all get the potty training eventually - I wouldn't worry about it. Her self esteem is MUCH more important that weather or not she is in diapers or undies. Trust me, she'll get there eventually on her own. Just be a patient, loving mama as I'm sure you are!!