Toddler is withholding poop!

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My 2 year old has been withholding poop for like 6 mos. I can tell when she has to go because she'll whine and dance around and then not poop. She goes maybe every 4th or 5th day. She has tons of veggies and water and isn't constipated. Has anyone else dealt with this? She's very good about peeing in the potty.