L.S.
If you're going through that many panties in one day she's just not quite ready yet. Yes, you could keep pushing her to the potty every 20 minutes, but what does that really teach? If you're forcing her to go and it becomes a struggle of wills and ultimately something unpleasant (ie spanking), she's not going to learn anything except that the bathroom is an unhappy place for her to be. It will only set you behind.
2 1/2 is really young so please don't feel that it's a race against some clock or artificial time line. She will learn when she is ready. They all do. It could be next week it could be several months from now. My only advice is not to push her especially if she's having accidents. If she's having that many accidents a day, maybe it's time to take a break and come back to the potty learning when she's maybe a bit more ready.