Is there anybody here who has a Facebook page for a group, who can pm me or discuss here some details?

It depends on the app she uses probably. There is a way to make posts in the group from what looks more like an anonymous administer rather than from the account of the administer. I’ll PM you also.

I believe that it’s a simple matter of “passing the reins” by assigning someone else (even a “sock puppet”) as admin/manager, demoting yourself, then leaving the group.