Keep with it. My son is finally potty trained as of mid December. He was 41 months old. He was very resistant. We tried all of the methods. He was the "king" of holding it.
We kept with it. Kept putting him on the potty every so often. Finally, one day out of the blue he walked into the kitchen and said, "Mommy, I have to pee." I told him to get to the potty. He did. From that day on he was potty trained as far as urine. About a week later, the idea of how to poop on the potty came to him. It was literally as if someone had flipped a switch in his head. One day, the ability to use the potty was off, the next day it was turned on.
We tried incentives. I think they helped. We used Hershey's kisses. One for urinating on the potty. 3 if he urinated and pooped. As I said, I think they helped. However, something had to be just right for him.
My best advice is to take a deep breath and know that you are not along. This is one of the most frustrating processes. To be honest, when I went through it with my daughter (now 8) I was never sure if she was ready or not. I went away for the weekend with my husband. She went to stay with my twenty something sister and my Mom for the weekend. My sister potty trained her in 2 days. The difference was that she wanted to do it for my sister. My sister created a potty training diary for her. They decorated it together and each time she used the potty, they wrote in the book. If she had urinated or pooped, they decorated the page with stickers as well. When I picked her up, after using the potty for 2 days, she wanted her diaper on. I refused. She resisted for a day or so and had a couple of accidents but within 3 days, she was wearing underwear all of the time (she was about the same age as your little one).
There are different websites and techniques for potty training. I did a search of the web. One uses a baby doll and shoes how the baby doll goes on the potty.
In case your little boy is younger, I have to say my friend's technique really worked for her and it could help you with your daughter as well. At about a year old, she started sitting the child on the potty for a couple of minutes after each diaper change. 2 out of her 3 kids were potty trained by about 18 to 22 months of age. If she is the older one and sees her little brother on the potty, she might get a little jealous and a little competitive to be the first one to use the potty all the time.
Anyhow, I hope my ramblings are helpful. I know it probably doesn't seem like anything is working but hang in there, it just takes longer for some kids (like my son) to finally get it. But when they do, it is not long before they are accident free almost all of the time (he has accidents occasionally when he isn't feeling well). I'm going to try my friend's technique for number 3 (he is 5 months old now). ;)