I'm taking it that you're going for a casual and relaxed walk. Setting aside the stiff neck, there is no motion in her shoulders and her arms are simply swinging back and forth. Arms tend to dangle to some degree based on the level of muscle control, especially if they're idle. Think military march vs a tired walk home vs casual walk through a mall.

Her legs aren't extending out and coming down on the heels. Right now they come out and then kinda slide forward on the toes. And there is no shift in weight as she brings her legs forward, no hip swing, like her torso isn't really connected to her extremities so it looks rather stiff. The whole body needs to be involved.

Check out this video of random people walking at the mall. The camera settles after a bit.

https://www.youtube.com/watch?v=o1Ye9f641Rg