It really depends on if she is a purebred paint and if you breed her to another paint.
If you breed a purebred paint and you breed it with throughbred bay, then there is a chance that the colt/filly may be bay or a pinto. If you did breed the horse this was, it's offspring would not be a purebred paint colt/filly.
Also, it depends if your horse has a colt. Your horse might have a filly. You can't really change that....it's at random=)