The fall that led to the end was:
The two sons of Huayna Capac plunged the empire into a brutal civil war. Atahualpa and Huáscar called on the mummified bodies of past Sapa Incas to assist them. The Incas believed their rulers were living descendants of Inti, the sun god. ... The civil war seemed to end in 1532 when Atahualpa's army captured Huáscar. After that, it led to the downfall of the Inca.
I think that "Coya" was Coya Cusirimay and who was the daughter of the Inca Topa Inca Yupanqui and Mama Ocllo Coya, and the full sister of Huayna Capac.
Hope this helps, have a good day. c;
