How are Elizabeth I and Catherine of Valois (Henry V's wife) related?

Elizabeth I of England was the great-great-granddaughter
of Catherine of Valois.

Catherine of Valois was married to
Henry V as you say.  With him, she had a son who reigned as Henry VI.  Some years after
Henry died, Catherine married Owen Tudor.  With Owen, she had a son named Edmund Tudor. 
Edmund Tudor married Margaret Beaufort, whose great-great-grandfather was Edward III of
England.  Edmund Tudor and Margaret Beaufort had a son who reigned as Henry VII.  Henry
VII, of course, was the father of Henry VIII and Henry VIII was, quite famously, married
to Anne Boleyn.  From their marriage came Elizabeth I.