Potty training question

I took the advice from you guys about 6 months ago (when my daughter was 2) to not force potty training and it’ll happen when she’s ready. Well, she is ready. She’s been using the potty here and there but today she complained her diaper was too tight and I told her the store doesn’t sell bigger sizes. I told her we could use those or she could use the potty. She wanted to use the potty. Great. She refused underwear, which was fine. She walked around with no pants on and she went twice in the potty. Then she pooped on the floor. This poop was the size of an adult Great Dane’s poop. HUGE. I told her no big deal, accidents happen and tell me next time she has to go poop or pee. For nap time, I put a diaper back on her (not ready for potty training during sleep yet - we have a 4 week old too and I’m tired enough lol). She got up from her nap and wanted underwear on. Amazing. She picked them out. Downstairs at one point she pulled down her pants and undies and ran to the potty but then said “I can’t go”. I told her to take her time and sometimes mommy and daddy have to sit on the potty for a bit too before we can go. She pulled her pants up and went on her way. After that, she peed and pooped her pants for the remaining of the day. I am so tired of her wearing diapers. Now I change my infants and her butt is so tiny and then I change my 2 1/2 year old and I’m like omg you’re huge lol. SO I’m assuming this is normal day 1 regression and to stick with it tomorrow? Any advice? PS - we have potty nerds (the candy) so when she goes on the potty she gets some nerds candy (not a ton). We tried the potty chart months ago and she didn’t respond to it at all.