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.
Incorrect. The monarch still holds executive power within Britain; it is not ceded whatsoever. Withholding royal assent is the equivalent of a veto. The parliament cannot stop the monarch from doing that, and the monarch is absolutely not duty-bound to rubber-stamp any and all legislation that comes out of the parliament.