If she's not a mix of one or both, then she's a poorly bred of whichever she is (according to breed standard anyway). I do see min pin in the body and muzzle, but her eyes look very very chihuahua to me. I'd guess probably a cross of the two breeds, but if I had to pick one or the other I'm leaning more towards chihuahua. If you're really curious, there are breed analysis tests out there that could probably help. Min Pins and chihuahuas look similar, but are genetically different enough that a DNA test should be able to tell them apart easily enough. If you're not that curious, then call her whatever you like and love her for the wonderful little soul that she is.