Jessie could have gotten up at any point in all those years that she was under the bed
Emily obviously was not in her room 24\7
Jessie could have got up and walked around when she was out of the room.
Jessie could have left at any time, since it was obvious to her that she was forgotten.
Jessie instead chose to lay under the bed, without moving for years hoping that Emily would remember her and hold her again.
She didn’t bat an eyelid about it.
Jessie waited. She waited so long dust gathered on her. She didn’t move even slightly or else the dust would have been disturbed.
She didn’t just go back to being a toy, since, as a toy, she would have been wide-eyed and smiling.
She just let her depression and loneliness consume her, she let it stay plainly on her face. She didn’t move for years. She suffered and watched and waited all that time, perfectly aware of what was happening around her. Jessie didn’t even move her eyes to watch Emily’s feet.
She just. Waited. Hoping Emily would hold her again but with each passing year, I imagine that her hope waned.