Both of these options are worse than not mailing banking information at all. Both of them are worse than encrypting properly, which, in this mom's case, means installing PGP.
Yes, in this case, bad crypto can make a bad situation worse: it can create a false sense of security.
And in the general case, bad crypto does much worse things than that. Logging in without a password. Flipping bits in a cookie to become any user on the system. Gaining admin privileges. Spoofing authorities to collect secrets from users.
Bad crypto does not care how horrible your mom has it. Engineering says, bad crypto is going to be bad no matter how hurt your feelings are.