The Queen can’t block it. It’s not a Constitutional issue, nor one that engages the Reserve Powers, so she has no grounds to do so. The Queen is a Constitutional Monarch, and Parliament has primacy under that Constitution - the Queen can only legitimately refuse assent to a law that exceeds Parliamentary authority.
There are 26 Church of England Bishops who sit in the House of Lords as the Lords Spiritual (other Lords are the Lords Temporal), and it is their role, if they see fit, to try and represent the Church, of which the Queen is Supreme Governor, in the Parliament. They do get to vote, but they represent only 4% of the current Chamber. And they don’t vote very often (they did vote to assist in stopping a Euthanasia Bill from passing the Lords in 2006).
Actually, it is a constitutional issue. Under the British constitution, one of the monarch's titles is Fidei Defensor, defender of the faith. Moreover, even though bishops of the C of E sit in the House of Lords, Queen Elizabeth is the head of the Church, superior to the Archbishop of Canterbury. If she were to assent to this bill, it would fly in the face of 2000 years of Christian doctrine. So the question is, will she uphold her royal oath to God or not?