Don't buy perfume unless you know what she likes.....I would think your son might have some ideas for a simple gift that she would like.
Be cautious with the pin. If she doesn't already wear something on her coat, it's unlikely that she's that interested in them. I've gotten my share of costume jewelry as gifts; however, if the giver truly considered my preferences, I would only receive dangling earrings since I infrequently wear any other type of jewelry.
I don't think the gift cards have to be thoughtless. For instance I wanted to get one of my employees a small birthday present. She usually talks about her 2 boys, but I didn't want to buy them anything. One day, she told me her favorite store is Jack's World - so, I got her a gift card there, instead of just getting Macy's, etc.
So, if you know of a store that she absolutely enjoys shopping in or if you know that the person is saving up to buy something big at a particular store, gift cards can be very thoughtful.
Whatever you do - make sure you include a gift receipt to allow her to exchange easily.