"I had read one of Mrs. Guinea's books in the town library - the college library didn't stock them for some reason"
Belle Bennett (Stella Dallas in the 1925 film)
Public DomainBelle Bennett (Stella Dallas in the 1925 film) - Credit: Photoplay magazine

Here the narrator, in her wittily sarcastic way, is suggesting that Philomena Guinea's books, whilst popular, were not renowned for their literary merit. We may probably assume that this is also Plath's view on the writing of Olive Higgins Prouty.

For an example of Olive Higgins Prouty's writing, try The Fifth Wheel (1916)