Other than the current obvious UX deficiencies of installing and using them, a client certificate might help people like your mother-in-law. But one would idea

Other than the current obvious UX deficiencies of installing and using them, a client certificate might help people like your mother-in-law. But one would ideally have a passphrase on their private key. If you can't remember a passphrase, the "something you know" portion of "something you know and something you have" is kind of out.