Answer: I have an idea that may work for her, depending on what she is planting. I filled the bottom third to half of my barrels with those styrofoam "peanuts", then placed a few sheets of newspaper over them (so the soil wouldn't filter down), and added soil on top. I was planting annuals, so they didn't need deep soil. If she is planting annuals or small perennials, she can try the same thing. If she is planting a larger plant like a shrub, then the plant will probably need the entire tub filled with soil.
I'd hesitate to mix the styrofoam pieces in with the soil, because they have a way of working themselves to the surface (like perlite) and looking funny.
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