My son is 3 1/2, and we just started another attempt at potty training (others did not seem to be working, so we waited until he seemed ready). At first he did the same thing your daughter is doing, and I have started just telling him he must sit on the potty, rather than asking. I say "time to sit on the potty" or "let's go sit on the potty." At first he balked, and I told him he could have a treat (he really likes yogurt-covered raisins) just for sitting for a few minutes. Sometimes he peed, and sometimes he didn't. When he peed, I made a really big deal about it by clapping and getting really excited, and he started clapping too. Now he usually pees right away when I say it's time to sit on the potty, although he still doesn't tell me he needs to go on his own.
So I would try just insisting that she sit, if not pee, and focusing on being really positive when she does pee and trying not to be too negative about the accidents.
It also might be that the prizes aren't motivating her. I was hoping that stamps or stickers would do it for my son, but that didn't seem to entice him at all. We ended up going to a local toy store and buying several small prizes for a couple of dollars each (I told him no more than $5, and I let him pick them out). Then we let him look at his prizes while he was sitting on the potty, and that seemed to work. Now that he's doing so well, we'll phase the prizes out (a prize for staying dry all day rather than each time he pees, for example).
If nothing seems to be working, though, I'd probably take a break and try again in a month or two. I just didn't feel like battling over the potty for too long, so when I was having to fight about it too much the previous times, I brought the diapers back out. I have to say that it has been so easy now that I've waited until my son is more on board with my plans!
Good luck!