M.S.
I would get rid of the pull ups and start putting her in underwear. If she is in pull ups then there is no reason why she would want to go out of her comfort zone and use the potty. She will mess in her underwear a few times, but if it is unpleasant for her then she won't do it very many times. The fact that she hides away in her room to go tells you that she is fully in control of knowing when she needs to go and is able to control it. Also, you need to have a reward set up for her. My son gets a hot wheel car every time he goes in the potty. It took a few months (he is 2 1/2) before he would go consistently instead of holding it until he had on his naptime diaper though.