Lorraine's mother has a very busy, responsible job as a care assistant, which doesn't leave her much time to prepare proper meals. In any case, she's not much of a cook, which is a characteristic she's passed on to her daughter. One day, Lorraine tried to bake a cake and her mother said it was horrible and that it was a waste of money.
As well as being more convenient than cooking, preparing canned food is also much more economical. In fact, the canned food that Lorraine's mother brings into the house is not just cheap, it's free. Without any moral qualms, Lorraine's mother steals canned food from the elderly patients she's supposed to be looking after.
Most people would find such behavior thoroughly objectionable, but not Lorraine's mother. She figures that she's entitled to take this food by way of compensation for the lousy money she makes as a care assistant. As far as she's concerned, she's just evening the score.
What this means, among other things, is that Lorraine and her mother never have an interesting conversation. As Lorraine ruefully reflects, good food is supposed to produce good conversation. But because all they ever consume is canned food, chop suey, and instant coffee, good conversation is impossible.