Well I've clearly missed alot of content, when in the world does bell disappear
When you are trying to Refurbish the Milk Sucking barn from time to time Bell, would wander off.
She has a Scene if you find her in Transylvania, and The Forest, just find her in the Jail at New Ark, if both locations fail to Piece.
Go to the Mall, should find a few stores find the store with the CowGirl tag to get Bell, a CowBell.