More important than the (probably negligible) impact a VP pick will have on the election is having someone who could be a good President if the President died or was killed. (That was Lincoln's big mistake in 1864, putting Andrew Johnson on the ticket.) Haley would never have a chance of being elected on her own because she wouldn't ever be able to convince people she would make a good President.
She is the only person on earth that can turn the south blue.