It's not assuming, it's inferring directly from what she has said. 'I'm sure he's blowing out to his family so I'll have to deal with their shit later too". That's not something you say when this isn't a normal occurrence or something you've had to deal with before. You don't usually spout totally irrelevant assumptions out with no bases like that. Then you add on that he's held money over her head multiple times in the past, because he earns/pays more than her towards their house/life and suddenly her responses, whilst wrong, all make sense.

It's not assuming anything, it's taking directly from her post and the various comments she's made in the thread