The abbey was restored to the Benedictines under the Catholic Mary I of England, but they were again ejected under Elizabeth I in 1559. In 1560, Elizabeth re-established Westminster as a "Royal Peculiar" – a church of the Church of England responsible directly to the Sovereign, rather than to a diocesan bishop – and made it the Collegiate Church of St Peter (that is, a non-cathedral church with an attached chapter of canons, headed by a dean.) The last of Mary's abbots was made the first dean.
When Elizabeth established  Westminster as a Royal Peculiar, what specifically did she turn it into
a non-cathedral church with an attached chapter of canons, headed by a dean