they can flip to Malachi
Seems an odd choice of book to me as it's easy to find, being the last one in the OT. Not that I remember it ever being quoted from.
I took JWdaughter's reference to Malachi as a general reference to any of the small prophet's or difficult to find books in the Bible. JWs are usually pretty good at finding any obscure passage, and to some it's like a badge of honor to be able to do so.
Malachi itself is rather easy to find since, as pointed out, it's the last book of the OT and comes right before Matthew. But the reference could have been to any other small book - Nahum, Micah, Amos, Obadiah, etc.
When JWs, such as the ones in the opening post, are dropped from voluntary service by the Organization it leaves them with basically nothing to fall back on except the ability to find an obscure scripture in the Bible.
'Try living on that' is the humorous reference I got from her post.