This isn’t great, but it’s what I ended up resorting to for my mom who refused to use any service, browser setting, or saved file:
-
Make a “master” password with upper-case characters and digits (e.g., M45T3R). Memorize it or write it down.
-
Interleave the characters with those of the domain the password is for (e.g., for google.com: gMo4o5gTl3eR). She can type the master password first, then put the cursor at the start and type each letter of the domain name hitting the right arrow after each letter.
As long as she remembered the master password, she could reconstruct the others on the fly. A human could still look at the result and figure out the pattern, but at least it protected her from automated tools.