Speaking from experience she probably no longer enjoyed interacting with you, found someone better to talk to, or she never enjoyed interacting with you but she had no one else. But eventually she decided to just **** it and stopped talking to you anyways because she didn't enjoy talking to you to begin with.
My best friend from 1st grade to 6th grade did this to me when he finally found a new friend. He found me to be miserable company because I was pretty damn boring. But he had no one else. He struggled to make other friends. He was stuck with me for 6 years. After he ghosted me, he went as far to vandalize my locker, carve my name all over the school with explicit embarrassing insults. Almost the entire school stigmatize me and made fun of me thanks to that. Best friend of 6 years from bitter enemy within 3 weeks. It happened randomly and spotaneously in an instant. All because I am a boring person.