She overcame all of her difficulties and created her own destiny as a merchant all by herself. That is not all. After making a large fortune, she willingly donated almost all of her wealth to her starving neighbors. I really respect her way of life.
Here, if i use was instead of is, the focus of the thing verb indicates would be changed?
1) That is not all. [as I tell the story now]
That implies that there is more to the story you are telling.
2) That was not all. [that happened to the lady]
That implies that more happened in the story you are telling.
So, it depends on how you want to express yourself. Both are right.
[please note: created her own destiny as a merchant is a bit much. Perhaps shopkeeper is better. And "created a future for herself as a shop owner"/
We use "that is" to give an example or a clarifying comment.
The word "that" is a dummy subject. It refers, in some way, to the current text or "What I am saying" (or similar) and so uses the present tense.
So could be understood as
She overcame her difficulties all by herself... What I have said is not all I could say...
