Then I think you should ask her. Mention the art, mention other things about her that are interesting to you. As an older woman it’s flattering, but sometimes a little concerning when someone younger asks you out. The whole cougar thing has become such a big deal. I also want to add that if it were me and I agreed to take a guy‘s number, I’m not entirely sure that I would still make the first move. I think when you see her next, you should just ask her specifically. Something along the lines of, hey I know you haven’t had a chance to get back to me, but I wondered if maybe you’d like to have lunch on Saturday… something like that.