Blocked Person Viewing my Posts in Group

A person I have blocked on FB is shown as "seen" on posts I make in a group. I had a friend use her FB account to go into group to see who this person is. The person is the one I have blocked. Under the Members of the group this person doesn't show for me, but her "seen" is there, showing as "one more" on my posts. Could the Admin of the group have done something to allow her to see my posts? This person is in other groups I am member, she cannot see my posts on any but this one group. Thank you for any help.