Not everyone who believes that a stone is healing power believes that they are ontologically basic.

But she is actually treating healing as an ontologically basic concept, even if she doesn't understand that she is doing so. That's enough.

She thinks it's possible for a stone to heal and do nothing else. It's not possible, unless the stone contains an intelligence that can determine whether a physical change made by the stone is "healing". It's every bit as absurd as having an acid that only dissolves shirts.

In practice she might tell you: "Duh, of course I check with a trustworthy spirit whether the stone is right for the particular occasion."

Does she believe that the stone causes harm if used in a way that doesn't match the judgment of the spirit?