"When bills become Acts (in other words LAW), she is handed a manuscript for assent and she signs off on it."

Actually the Queen has never done that. I believe the last to do so was Queen Victoria in the 19thC. Royal Assent is basically a formality given by various means both ceremonial and the normal day to day where certain members of parliament, who have the authority to do so, simply state that assent has been given. It is in reality nothing more than a term to signify that the bill is done and dusted. Since Great Britain was created Royal Assent for UK legislation has only been witheld once. That was by Anne Stuart in 1708.