She looks too refined in the head to be a shetland or chincoteague. She could be an arab mix pony or perhaps a welsh mix? She could have shetland in her mizxd with something else to help refine hear features. Pinto/paint comes in many breeds and really isn't an indication of her heritage, although she could be a welsh/paint mix by her features. She's cute. Would be easier to tell with another horse or something for reference to height etc.