Re: Should I do it?
Sometimes even those who perform all their Salaats, recite the Quran daily and spend their ‘free time’ learning about religion and devoting it to their faith can place their faith in such things. She may honestly believe that as she has such a firm hold of her own faith (reciting Quran etc) that having such a thing for protection isn’t wrong.
Some Muftis/Sheikhs allow it as far as I’m aware. I guess it boils down to which Imam/Mufti/Sheikh she follows.
Also; as it’s your SIL I support the others on the idea of remaining quiet. If it was your own sister I’d say talk to her because you know her well enough but in such a case it maybe worth staying quiet.
Isn’t there womans lectures held at an Islamic centre near you on the subject you could both attend? Just as a way of insight into the subject? Just a thought.