I would also have to disagree with the idea that it is just normal kids sorting out time, tense, etc.
When your DD talks about when she used to be big, ask about what she remembers, it might be a very insightful conversation.
When my DD was in the 18 months to 2.5 y.o. range she loved all things Japanese. We had a channel on TV in Costa Rica, and we were flipping channels. We flipped past an animated Japanese TV show, and she whipped around (her back was to the TV) and quickly became very engrossed in the program. She had never heard Japanese before, but seemed drawn to the show. (she still does have a leaning toward Japanese, but it has certainly lessened). This may be an indication of a former life, I don't know.
But, I agree that children are more open and in tune to these types of "memories". What the religious call a soul, I would contend is really just life energy. And as we know, energy never dies, it only converts and changes shape. So our children could very well be in tune with former "life energies." (I suspect I was Spanish in a past life, but that's a different story).
And now DS (2 y.o.) says he sees ghosts. He burst into tears at the dinner table last night, and when he calmed down, he said he had seen a ghost in the door. We asked him questions and he said it was a green man. Don't know if there's anything to it... I'll have to keep my eye on the cat and see if she sees anything
In short, I would lean toward your DD being in tune to something unique, and not so much just going through normal toddler language sorting. They may confuse tomorrow, today and yesterday, or breakfast, lunch and dinner, but talking about when they were big, or when they were someone's mommy... It's like dreams, you can remember them when you've first woken up, and then they fade. Ask her about it now, before it fades