If you tear that tank down and clean the beans out of it, you will lose whatever cycle it has left in the gravel. You already changed the filter media which removed most of the cycle already.

These fish simply do not belong in that tank. No goldfish does. If she wants fish, she should have a school of tetra's that will work in that size tank. Does she add dechorinator to the water to remove chlorine?

"She's 70 years old, so she doesn't know any better."

Ahhhh....so am I (in 6 months) Sounds like it's OK to be stupid because she's old. LOLOLOL