You're absolutely right about the way that Julia is being written here, alwaysdavid. She comes across as somewhat of a shrew here, not the devoted family friend at all.
She and Barnabas seem very annoyed that the family doesn't seem to be taking their prediction for impending disaster all that seriously. But they haven't really offered much in the way of proof, other than that they are Barnabas and Julia and their word is enough. Perhaps if they had been a bit more honest about some of the stuff from the last year or so, they might be able to persuade the others.