Does it have to do with size instead? Like when she reaches 4' 3" she becomes something other than "The Baby"? Because she's growing so fast she might reach this particular factor before I am ready to stop calling her that.
I was cleaning out a closet a couple of weeks ago and pulled out her bouncy/vibrating seat. She did a big "ooohhh" when she saw it. We dug out a couple of batteries and she climbed in it and kicked back in her massaging bouncy chair and just sat there. Clearly, she was not going to give this seat up again.
I watched her sitting there. Head over the top. Arms dangled on the side. Feet flopped off the end. I remembered placing her in that very seat just days after coming home. I remembered I had snapped a picture of her. Long, skinny little arms and legs.