This is very dependent on the individual and less to do with being a 65 year old female.
- If you're going with Perfume - find out what she wears. No one on this could really suggest for someone that they don't know.
- Only buy a scarf if you're familiar with her style. I can't buy clothes for my mother, but my sister can - I get it wrong!
Here's some suggestions, but very dependent on what she's interested in:
Garden - a nice plant, I'm not thinking a 7.99 potted plant from tesco's. But something like a bay leave tree, or something for the garden Something that's low maintenance - or very minimal, but gives pleasure. You would need to have seen her garden to know if this would work.
Food - IF she enjoys going out with the ladies for lunch, etc.. then vouchers for the westbury, or somewhere like avoca, etc... can be nice.
Beauty - others have suggested the hair cut/facial/manicure - these are good, BUT only if she likes them. Many don't (speaking as a female!)
Culture - IF she likes music/theatre/art, tickets to go to something that she's interested in.
Why not ask her, or at least hint?