I have a friend who likes to oil paint. I don’t know anything about it, what are some things I could get her that she might need?
Actual paint, it can be fairly uncheap. Real pigment paints, like proper aquamarine etc. The good stuff (artist’s colours), not the student oils. Windsor & Newton are an OK brand that should be easy to find anywhere.
Brushes are less of a deal with oils versus watercolours, but they are never unwanted.
Maybe some good linseed oil, or real turps.
They may not like the smell of real turp. (I do, it makes me think ‘Now I’m PAINTING!’ but some painters don’t.) I’d go with a few nice tubes of a name-brand paint. A BIG tube of white (you never have enough white paint, I go through it like it was 2% milk) A good strong blue, like Thalo blue, or maybe a burnt umber. You can’t go wrong with your basic paints.
Even if he doesnt often use the colors, he’ll like having them around.
A beret.
A lab coat.
Artists are supposed to suffer, so maybe you could steal your friend’s car. 
Perhaps a gift card to a really good art supply store? That way, she might pick out things she really needs.
Ditto the gift card. Artists tend to be loyal to certain brands, and you have no idea what she really needs anyway. I’m an artist, and after years of trial and error, I use only one brand of paint, one brand of brushes, etc. Do her a real favor by finding out where she buys her supplies, and give her a gift card.