I agree that there are certain paths where this is/might be true, depending on what you did before. But I had a wild Holly at the beach trip who is still clearly interested in Ian.Actually during that scene with Ian when they were smoking weed. She tells Ian that she now feels the same way about Lena, that she USED to feel about him. Which is a further indication, that she's no longer crushing on him.
You're right about Robert though. For some reason, I thought Ian or Lena had talked about Robert with Holly, after their fight during the life drawing event. But even so, her having sex with Ivy, Mark and now Robert, all at the same time, is further evidence that slutty Holly is over her crush with Ian. And that her flirting with him now, probably has some ulterior motive.
AFAIK there is also a path where wild Holly comes together with Ian around chapter 10/11 and they hit it off. So far I could not get it, I just heard that this is a possibility. I don´t know how wild Holly keeps on getting when Ian/Holly come together around this time, but there are options. The pic shown by saltynip wild Holly together with Ian and getting closer "so naughty ... only with you... for you" there might be a path in the works about this.