First, the percentage of women who have had a lesbian experience is high, probably 60%, though the rate of those who stay lesbian or admit to the experience in polls is far lower.

Second, you're right, in some cases it may be triggered by trauma, but I know a few lesbians that are just lesbians, and self-employed conservative ones at that, and I'm in California.

In either case, it goes to show that going lesbian is within the realm of possibility for women given the right conditions.