Toddler only poops during her nap and bedtime. Help me, please.

My kid (almost 2.5) is doing great with peeing on the potty. She's still not telling us she needs to go, but we have very few accidents and some nights she stays dry overnight. However, pooping is a monster of it's own. She will hold it for 2 or 3 days, become extremely clingy, and refuse to even sit on the potty to pee. She's had a few pee accidents because of it, then she holds the poop until bedtime (diaper) or nap (undies) and poops. I don't think she's doing it purposely, she just relaxes and can't hold it while she's sleeping. But she's terrified to poop on the potty.We've tried rewards, and she's pooped 3 times on it, when I just managed to catch that "look" and get her on the potty in the nick of time. And she knows she gets a piece of chocolate and looks forward to it. I've tried showing her (with playdoh) how the poop comes out. We've tried putting her on the potty with her favorite show, which is a special treat, and she's so focused on that, she's a zombie and won't poop.We just started her on a 1/4 dose of miralax to make it harder for her to hold it for days and become so uncomfortable. I think once we catch her and get it in the potty a few more times she'll realize it's not a big deal. How do I get her to overcome this fear? via /r/Parenting http://ift.tt/2eiCXN3