Complex sentence: Rainie demands to know why Tanya stopped her treatment, so she explains that it did not work for father and confesses she helped him die, which shatters both Rainie and Cora.
Split into simpler sentences: Rainie demands to know why Tanya stopped her treatment. She explains that it didn't do their father any good and confesses she helped him die, which shatters both Rainie and Cora.