Keep in mind that food as a percentage of one's budget was considerably higher 150 years ago. For that family size she probably paid at least 1/3 and maybe up to 1/2 of her income on food, plus clothing for growing children and school. Seems unlikely she'd be able to afford significant vices of any kind, if that is your implication.

Here are some family budgets from the 1880's, just to get a general idea of the type of expenses she might've incurred:

http://historymatters.gmu.edu/d/5754/

I'm also keeping in mind her husband's pension gave her income equivalent to a fairly typical lower middle class salary in Britain at the time, when families of seven children were not uncommon, and most families lived on a quarter of that income. Most people spent up to half their income on food, but most people didn't have a combination of well above average income and claimed inability to afford more than intermittent consumption of animal food even after cutting back on all other areas of expenditure and supplementing income by selling off old valuables.

"Vice" is one reason why somebody receiving well above average family incomes for the time could have a well below average ability to feed her family, indebtedness a more likely one, not actually receiving her pension [consistently] is a third. But the most logical reason for her reporting conditions of extreme poverty (in between gripes at loss of middle-class privilege) despite being entitled to a pension worth 4-5x the average wage of the time is that she is exaggerating the hardships in a letter which is essentially begging for help.