I agree with your points about Mrs. Miggins. The difference being that she would be far better off if you simply handed her the posting key and told her to treat that like she does her facebook password. Also, let her know that once she accumulates some significant value in her account, she will need a different password to allow her to manage those funds. This is far better (imho) than giving her a single owner key that does it all (because of the risk that she will treat it like she does her facebook password and when it gets hacked she has lost far more than explaining to her friends why there are lewd posts on her facebook page).
Once she gets to that point (of having real value tied to her account), she will then recognize that the 'money password' needs to be more tightly controlled than the 'posting password' (and thus will be ready and willing and informed when it comes to accepting custody of that key).
Yeah - that makes sense to me. The language you use there is really good too.
Trying to put myself in Mrs Miggins head (there's a lot of soft sofas and fluffy cushions. With cat pictures on the wall), having a posting password that lets me manage my community, and then a separate money password to manage my funds not only feels understandable - but sensible.
👍