Help! Potty training nightmare!

My daughter will be 3 in April. At around 2-2.5 she was great at going potty and was very motivated. She would pee and sometimes poo on the potty whenever we would take her, but never announced she had to go so we didn’t push it. Her younger cousin became potty trained recently and they spend a lot of time together so you would think that would motivate her further, but it’s done the opposite! It’s like she’s regressed with potty training. The past month or two she’ll smile right at me while she’s peeing in the diaper, she paints with her poop during nap time, she has no problem peeing in her underwear and splashing in the puddles she’s created. I’m worried I’ve missed the window of opportunity to train her and that she won’t be potty trained until she’s 4. Incentives like candy, stickers, praise, etc won’t work. She’s really smart, but really stubborn too. Does anyone have any advice?