To be clear, there is ZERO reason to believe that the woman in the story is a lesbian and there is no indication she identified as such. In fact, the only way this story makes sense is if she is not a lesbian and doesn't consider herself one. Lesbians who have come to accept their lesbianism simply do not experiment with penises. She willingly had sex with someone she knows is not a woman and who has a penis, and doesn't appear to have felt pressured into it or traumatized by the experience. She, like most straight and bi women, just didn't like it. And it's pretty clear by implication that she was expecting a penis ("But if I wanted to have sex with a legitimate woman, I'd be expecting a vagina").

In fact, she considered the experience straight/heterosexual, which it factually is. She just didn't have a good time and doesn't want to have sex with another trans woman. The only way the story makes sense is if she is and considers herself to be straight or bisexual. Most bisexuals still just want to fuck regular men and regular women and avoid the mental gymnastics and emotional labor. So it's entirely possible that a bisexual woman would give a trans woman a try before deciding hard pass.

However, it is equally plausible that the woman is straight and maybe was curious about the situation or is trying to make a point that the women who have sex with trans women do not see the experience as lesbian (which it's not). She gives no indication that she's actually attracted to women. The closest she gets is by saying, "But if I wanted to have sex with a legitimate woman, I'd be expecting a vagina," which is entirely a hypothetical and even arguably implies that she doesn't want to have sex with a "legitimate woman."

In any case, I don't think this woman is an idiot. Her diction indicates that she is being clever about what she says and is not saying. I think she got exactly what she signed up for. She wanted to experiment and either confirmed that it was not for her or made a point to a colonizing trans woman.