I don't like Lisa Diamond for a variety of reasons but to be absolutely fair, she did say this in her book about fluidity (Sexual fluidity):

If we examine correlations between women’s initial percentages of same-sex attraction (in 1995) and the size of their subsequent changes, we find a strikingly consistent pattern: the more same-sex attractions a woman reported in 1995 (and, in fact, throughout the rest of the study as well), the less her attractions changed over time, in either direction. Thus women who reported predominant or near-exclusive attractions to women in 1995 tended to remain pretty much the same. The women with more nonexclusive attractions—those who identified as bisexual or unlabeled—underwent the most sizeable shifts."

And this:

"If we use these changes in attractions to make inferences about changes in sexual orientation, we must conclude that there is not much evidence for change in orientation. The small shifts experienced by lesbians nonetheless kept them in the lesbian range, and even the sizeable shifts experienced by unlabeled and bisexual women kept them in the bisexual range: they almost never jumped to near-exclusive same-sex attractions or plummeted down to nearexclusive other-sex attractions. Note, in particular, that the women who had reidentified as heterosexual by 2005 did not undergo much change either: they had always reported less frequent samesex attractions than the rest of the sample; they simply came to label and interpret these feelings differently over time."

And lastly this:

"The only group of women who showed extreme stability in their identity labels over time were the women who basically described themselves as being 100 percent attracted to women from the very beginning. They showed almost no identity change. So it was very clearly connected to this understanding of your own capacity for different types of attractions and behaviors over time."

So even she's saying that completely heterosexual and homosexual women exist. The point of her research was to prove that bisexual women were real and were not a phase like many people thought at the time. However many people twisted her words (and imo she let them do this or encouraged it) and used the study as proof that conversion therapy could work, or that lesbians weren't real and not much press was given to those things I quoted in her book.