I would think about things she likes or hobbies. If she is/was a gardener, a garden party. Or a tea party?
Hi this is Peggy. Here are some ideas for her 80th birthday party. Hope you have a great time. The Best Themes, Decorations ... - 80th Birthday Party Ideas
Find festive themes, party decorations, games and tips on how to celebrate an 80th ... 80th Birthday Party Ideas for Women - How fun is this pink, black and gold.
Find pictures of her growing up and incorporate into decorations in her favorite color. If you can find a few good pictures, blow them up or do a slide show.
Lots and lots of balloons! A giant 80 in balloons!
Here are some cute ideas. https://www.80thbirthdayideas.com/80th-birthday-party-ideas/