A violation of the first principle of fiction writing - Show don't tell - in The Lowland

The next section of Jhumpa Lahiri's The Lowland involves a return to Calcutta and to Subhash's family - we see his mother, now quite a bit older, tending the memorial marker of her murdered son, Udayan, which sits at the edge of the lowland swamp, trashed every day with debris and other detritus. She is now widowed, and much of this section involves her recollection of the last years of her husband's life, as he gradually retreated from life in his own form of mourning for Udayan. She also feels regret for her estrangement from her surviving child, Subhash; she had told him and Gauri, now his wife, that they should never return to their homeland, and now she regrets this estrangement - she has never met her granddaughter, Bela. This whole  section is told by an omniscient narrator - a very long section telling us what the mother is thinking, without really much action at all in any way, which makes me wonder why Lahiri has strayed so far from the basic principle of all fiction writing: show don't tell. She rectifies this problem to a degree as the section moves along and Subhash and daughter, Bela, now about 12 years old?, not clear, make their first return journey to Calcutta. At least more happens in this section - as Subhash mourns his father's death, as he and Bela take several excursions into the city, as she begins to understand more about her family background. The two great unspokens in this section are: where is Gauri? and : when  will Bela learn that Subhash is her uncle and not her father? Subhash's mother at various times either intentionally or inadvertently is about to tell Bela the truth, but this  fact hovers just a little beyond the perimeter. As to Gauri, I for one was surprised to learn that she is still married to Subhash, now pursuing a doctoral degree, and I wonder why neither of them  has been substantially changed by their many years in the U.S. One should leave the other, for sure. This the section of the novel, though nicely narrated, would be stronger by far if it were giving us information we didn't have: we are not really learning much new here, just waiting for ticking bomb to go off, for Bela to learn the truth about her family, and to see what the consequences might be for  her and Subhash.