She held the power of royal prerogative but couldn't ever exercise it because Parliament retains the right to dismiss and choose a new monarch anytime they like.
The issue of royal prerogative was settled in the Glorious Revolution when Parliament decided it didn't like the King, James II and just selected a new one.
Every year we remind the monarch at the State Opening of Parliament that they can't ever use their royal prerogative.
The monarch might have influence but ultimate power rests with Parliament.