Can anyone help with potty training?

My daughter is 2 1/2 and has been diaper free since January. She did GREAT for a while. It seems lately she will wet her underwear just a little and then run to the potty. Or she will just let loose and empty her bladder in her pants. We encourage her to go potty every 2 hours or so depending on how much she has had to drink. Often she will have a minor meltdown because she doesn't want to go. What do I do? Go back to pull ups? We tried letting her go when she wanted to, but that just backfired. We offer an m&m when she pees or a mini marshmallow when she poops. I really want her to succeed. Thanks for your answers.