If you have a problem with cobwebs, I highly suggest this. There's even a light bulb attachment. I use it outdoors around the house to knock down spider webs, and wasp nests all the way up on my second story windows.
Some companies sell dusters with extenders (“telescoping handles”) that are meant to be used to clean ceiling fans. You and your grandmother might be able to adapt one to clean her bathroom!
Edit: New link here.
Apologies, Mod!