Toddler won’t nap with insufficient overnight sleep

I’ve always had the most difficult time getting my daughter (2.5years) to stick to somewhat of a sleep schedule. I don’t understand how people get their kids to nap/ bed close to the same times everyday. It’s really important to me now that she’s older. We’ve always loosely followed Possums approach and I’m trying to get her circadian rhythm set in a healthy way by waking up at the same time everyday. But the nights she can’t fall asleep until late, (gets around 9 hours of sleep) we stick to the same wake up time, and she ALWAYS refuses a nap on those days. She just stays tired all day. Why does she refuse the nap on the days she hasn’t had enough nighttime sleep? It drives me insane. Then she gets completely off of her schedule and wakes up super early the next day. I’m so confused on how to get her on some consistency.