It's hard to imagine what Karai... what Miwa will go through when it finally comes out. Imagine every memory, every thought, every feeling and every action in your entire life being revealed to be an ugly lie perpetrated by the man who murdered your mother and tried to trick you into murdering your own father. It is even money if her mind can handle it or whether she simply goes mad.
Leo already knows. Splinter told him at the end of "Follow the Leader". I can only imagine how Raph, Donnie, Mikey, and April would react when they find out. When Karai finds out (don't know how she will, but she WILL) she will HATE Shredder!