In the preview she says something like ""Clara Oswald has never existed" what if even the original Clara was a splinter from herself and was never was supposed to exist.

could be.. I think clara the original clara ihas always been someone else.. The Clara we know is superficial in that sense..

would explain the lack of depth to her character as well..

Do you mean like a time-loop paradox?

Like if a time machine came from the future you wouldn't need to bother to invent it because you've already got one?

More like every Clara ever was created from her including herself so there was never a original copy in the first place.

Ah sorry.. No I think Clara has an original copy but the ones we've seen are splinters.. There has to be an original??