I agree. She had an opportunity to show leadership in vetoing it, or whatever the analogous term is in GB. I was an admirer of hers—until today.
Sorry. She doesn't have a veto. The monarchy is ceremonial; the crown ceded its executive power to Parliament ages ago. Passing laws is Parliament's prerogative. The Queen's duty is to formally ratify it.
In theory, the Queen (and her viceroys, the various Governors-General of the Commonwealth countries like Canada) have rather broad reserve powers that they can exercise in times of emergency or constitutional crisis. This includes the ability to refuse to give royal assent. In practice, these powers are almost never exercised, and when they are, it's usually very controversial.