I've written two Betty-centered fanfics over the years. I didn't post them here, because the language and thematic content would be inappropriate for this forum, but I did post the links here, so I'll do so again:

Betty Cooper: This is Who I Am (from 1999) - Betty is forced into making a decision that will change the course of her life (and those of everyone else in Riverdale) forever - http://ldloveszh.tripod.com/mark/betty.html

Betty Cooper: Woman for All Seasons (from 2011) - the sequel; not as traumatic or blunt as the previous story, but much longer and fuller; follow Betty through her senior year of high school as she deals with life, love, and friend drama - http://ldloveszh.tripod.com/mark/betty2.html