Twins one has one kidney the other has two?

Strange question for you I have been told I only have one kidney n have type 2 diabetes I was born like it n my twin sister has had a scan n they confirmed she has two kidneys n doesn't have diabetes what I want to know is how this possible that she has two kidneys n I only have one We where born a month early n I was the weaker one out of us if that has any thing to do with it?? Love to hear what u think