Skip the black/death related ideas that so often come with 50. Depending upon her personality and the personality of the office consider the following ideas:
Think about using gold, like a 50th anniversary.
You could give her 50 gifts (some will have to be little ones, like 50 pennies or a 50 cent piece, 50 balloons).
You could give her all "golden" gifts: gold coins (those foil covered chocolates); butterscotch candies; a yellow rose, etc.
Or everyone could chip and get her a nicer golden gift (watch, brooch, nice pen, etc)
Or do things from her birth year. 1962 is a very cool year (I should know!). There's a lot out there...play 1962 music in the office all day...Everyone dress like in 1962, decorate the office in little "facts" about the year, etc.
Being remembered in a kind, fun and thoughtful way will feel good to her.