The only thing I can be sure of is that I have been.
I can't even be sure of the fact that I am, because by the time I can process this fact through the circuits and loops of consciousness, "I" is long gone. But that I have been is certain. Having been in this sense is the surest kind of being.
The trick though is not to get caught by it, not to assume that "you" that have once been is the same "you" that are now.
She is, in fact a very different person. She was once you, but she is no longer you, for you are not your past. The choice for who you want to be in this very moment is yours. But this choice can be much more informed, much more conscious if you take time to talk to the myriads of your previous selves.
Before you do that though, you have to let go, you have to forgive them all. In fact, I don't think you can (or should) talk to anybody unless you forgive them completely, unless you learn to listen and appreciate them as they are. This applies to your old selves as well.
Once you've forgiven them for not being who you want them to have been, once you are not embarrassed by them, once you have empathy for them, you can find that they have a lot to offer. Your previous selves can give you a different perspective. They can remind you of things you have forgotten. They can challenge your assumptions with more credibility than anybody else.
Forgive them, listen to them, learn from them.
And then forget them. For they are gone and you are in this very moment.