If you can stretch is out depends on how often she is going. So if you are taking her every 30 minutes but she is only going every other time then you can safely stretch it to every 60 minutes, if she is only going on average every 3rd time then I would think you could stretch it to every 90 minutes.
Always be sure to offer lots of praise when she uses the potty successfully. Also I would have DD help me clean up all accidents. And we did a sticker chart. I wanted the stickers to be the immediate reward so when we first started and she had a lot of accidents i would give a sticker each time she went on the potty and 2 for pooping then after XX many stickers she would get a bigger reward (ie a toy or a new book, or go out for yogurt, she always knew what the next larger reward would be) as she was getting more successful I didn't want to be giving large rewards often so I changed it to a sticker for every day that she didn't have an accident then after 15-20 stickers she would get a larger reward.
I would also let her pick out the sticker and put it on the reward chart.
Mama to my sweet lil girl (Summer 2010)