Is Tamura the original Homura?
Well, after the volumen 1 and 2, we can assume isn't Homura, because in one of the timeflows she find the one of the Mami's who was crazy and try to shot Madoka.
Beside, Tamura look like she have more empathy than Homura (just remember the dog and her new shield or her encourt with Mami)
But we can't assume nothing until they show us the original timeflow of Tamura