I don't know that they make their teeth fall out, but Hartz products are in NO WAY effective. At 6 years old, her teeth should be perfectly fine unless you've neglected then her whole life which I highly doubt you have.
You seem like a good momma! I'd take her to your vet and have her checked out. Dogs can get gum disease and other things like that just like we can with our teeth and mouth. Keep us updated on how she is!