This bug is two parts:
1) Create a Senior Personas Reviewers group. ("Personas" only because that's consistent with the current group name)
2) Make all interactions with the Flagged queue (including the link to the flagged queue) only accessible to people in that ^ group. Flagged queue is https://marketplace-dev.allizom.org/reviewers/themes/queue/flagged
Rob Hudson is a groups/permissions pro and can help with any questions.