Startup employee put on PIP but no documentation

Hello viner, A co worker of mine has been put on PIP by the company HR based on her managers feedback. Even though she got an average rating ,she did not get along well with the Manager and he got the HR to put her into PIP. HR here mostly follow what department leads tell them.

But there are some discrepancies :

1. HR has not formally sent her a email informing of the PIP procedure. This is all verbal
2. Her manager also hasn't given her any concrete milestones. He just said that she will be judged based on the feedback from fellow co workers.
3. Of late, the HR has been forcing her to resign even though the final date of pip period has not been reached.

Is this the normal PIP procedure followed in your companies too? Or is there something suspicious here?