If you put effort into representing yourself well, this could be a good opportunity, but I think that depends in large part on how honest she's going to be about it. A documentary maker can convey pretty much any impression that they want to an audience by selective editing and arrangement of the footage. Some documentary directors will go all out with this (Ben Stein, to pick an available example,) but even if they're not consciously intending to slant the delivery, if the director has an agenda going into filming, it can have a significant impact on the final product.

If you trust her intentions, then I think participation would probably be a good idea, but if you have doubts that she's trustworthy, it's probably a bad idea no matter how well you think you can present yourself.