So you have to tell her what you’re doing, but you don’t have to absolutely bury her in “woo woo”.
“Grandma, new studies have come out that some frequencies in audio address certain health conditions. I can show you if you’re curious at any point. Either way, I have an audio file here that was specifically designed to address cholesterol levels and ask that you at least let me play it for you a few times to humor me with the intent to fix your cholesterol.”
If you can’t get an agreement from that, free-will is a thing and even if you did play it, she would subconsciously reject it.
The important bits of the statement or something like that: 1) None of it is a lie even if it is a tiny bit misleading (studies have found that various frequencies address certain health problems, this audio file WAS designed to fix the health problem but not in the way that was implied), 2) she’s informed the file is going to be played “with the intent” to fix her cholesterol, her agreeing to that should lessen any subconscious push-back.
Now, I’m not an expert, so wait for others to weigh in before you try it this way.
points at figures’ post