If she has been married she could live off her husband's SSI instead of her own (assuming that the husband is no longer among the living). He might have contributed more and thus she would be able to receive more.
I didn't comment on it, but I noticed the absence of several words in what the DU OP quoted: "Husband", "Children", "Family". Nothing wrong with being single and childless lifelong. I had an Uncle who was both. But, using him as an example, he got a technical education and, with an interruption for WW2 service, he had a single-job career at a sugar production plant as plant engineer. His retirement was comfortable because of those and other related
choices.