I highly recommend a sportbrella. You can use it as a standard beach umbrella or use it as a beach shelter. We live near the beach in Florida and it's easily the best shelter/tent/umbrella we've bought. It's good for camping and sporting events also.

If your grandmother can't take the sun, I'd bring something just in case. It gives you the freedom to not have to worry about sticking to rentals. You can go set up wherever you want.