If your daughter is not both physically and emotionally ready to potty train and you try anyway, you will be frustrating both of you. Remember, every child is different. Just because her older sister was easy to potty train does not mean she will be easy to potty train.
My pediatrician told me that the best indicator that a child is physically ready to potty train is if he/she wakes up in the morning or from naps consistently with a dry diaper. This means that the bladder and spinchter mucsles are developed enough to hold everything in until the child is awake. I waited until my son started doing this before I tried to potty train him, and that didn't happen until a month before his third birthday. When I saw that he woke up with a dry diaper I would put him on the potty to teetee. I think this helped him realize what the potty was for and that he could teetee in it. I did this for about 2 weeks before I started to potty train him.
Yes, my sisters teased me that my child would be in diapers forever because I waited longer than they did, but again every child is different. Some mothers may even see it as laziness on my part because I didn't try to potty train my son sooner, but I don't care about that. I believe that I made the right choice because I instilled in my son a feeling of success and accomplishment with potty training. He had very few accidents. If I had tried too early I could have instilled in him a feeling of failure and shame with accident after accident. Who wants to do that to their child???!!!
One more thing, I found that pull-ups kept my son just as dry as a diaper, so he never realized when he peed in them. I would recommend putting your daughter in panties. This way she will know when she has wet herself, and she will learn faster what the sensation is signalling before she goes.