Authorship Guideline for unused experimental results I am a Ph.D. student and an intern worked with me on a project that is going to be submitted for publication in a prestigious conference.

However, the work that this intern did is not being used up in the paper. It was a supplementary experiment (not strongly related to the core contribution) which could not be used up since the final results appeared to be too obvious and did not add much insight. Also, this being a conference, there are tight restrictions on the maximum size of paper, and we are struggling on the borderline. Hence, it seemed prudent to leave out the said experiment.

With all the results being thrown out, there is now a moral dilemma about authorship of the intern. Me being the first author, I have a say in this matter and my supervisor has not intervened so far. It is likely that what I suggest/recommend will have an impact on the authorship decision. It is true that this particular person has put in considerable hard work to do what was asked of her and it is entirely unfortunate that those data are not being used up in the final paper. I feel bad for her, but at the same time,  as it stands now, there is no contribution of this person in the final draft (except a few grammatical/typo corrections etc.).

From my understanding, simply mentioning her in the acknowledgement seems to be a bit disappointing, but the most appropriate thing to do. However, I would like to ask the broader community, what would be the proper academic etiquette in such a case?
I think in a larger sense your intern certainly did contribute to the project... whether or not the specifics reflect that. They were part of the team. Many things in team work are unpredictable... but everyone on the team should get credit. Otherwise, think of it, people will not agree to participate and exert effort in situations where they're not guaranteed a good PR outcome. That attitude would wreak havoc with genuine scientific/intellectual inquiry.