Potty training help

Please give me all of your potty training tips! My daughter will be 3 in January and started using the potty at 18 months but she won't use it consistently. Today she peed twice in the potty and a while later I asked her if she needed to go again and she said no then came over to me 5 minutes later with her underwear full of shit and pee. I'm getting so frustrated. She usually pees fine on the potty but not poops. I'm at my wits end and we've tried so much. She tells me she wants to be a big girl and all done with diapers but then poops in her underwear when I let her wear them 🙃😅