It seems this may have have actually been a small street (or court?) off North-street in Barking, in an area apparently cleared in the 1930s, not a hostel or similar. While an unusual street suffix, there are some around even today (there's a Victoria Retreat in Cheltenham, for example).
Found some snippets in
http://www.britishnewspaperarchive.co.uk/St. Johns-terrace. North-street. Barking, and 13 well-built houses in the rear, known a. 1 to 13. St. John's Retreat. North-street. Barking. Essex
.
From other snippets it seems the residents were dock labourers/stevedores, a woman mentioned as a servant, etc. It is likely that each "house" packed in several different families to make the rent more affordable.
She may have had some charitable support to begin with, given the nature of her husband's death - sometimes at the end of an inquest report you'll see a reference to "a collection for the widow". Of course, that only would have gone so far. Otherwise with family support and some work of her own she may have been able to struggle along for a bit - but certainly remarriages were usually out of hard cold necessity on both sides - widowers with children also had the issue of finding someone to look after the kids while they worked.