Of course I wouldn't tell her, I built her that way for a reason!
More seriously, I suppose that depends on the circumstances. Proving it would be difficult, and even if I could do so, the revelation is likely to cause her a great deal of pain.
I would prefer to let her know, and ease the blow as best I can. From there, we can move forward in terms of making the best of the situation. It would certainly be interesting to see how her life can be improved without the limitations of passing for being a mere human.
But if I decide that revealing this would do far more harm than good, I'd stay with her as if nothing had changed, largely because nothing indeed has changed. I don't care about a person's heritage and nature save in terms of how they let it influence who they are as a person.
Either way, I would also like to track down whoever made her and find a way to get my hands on that technology, turn it to better purposes than effectively brainwashing sophonts into living a lie.