Many, many students, who ultimately got little credit for their work, worked many hours on that exhibition, but Julia gave no notice to that. Because Julia was a good and talented person. Letters of recommendation are not the place for working out such differences. They are the place for presenting an authentication of the individual's strengths, what they can and do do well. I once watched an admissions committee debate the admission of a candidate they would not have accepted otherwise, but a professor had written such a negative letter of recommendation, they were considering admitting the student just to see for themselves what could have prompted such a letter.
People are people.
They are complex and curious. They see the world and accomplishments differently. Julia had many wonderful qualities. If an employer could see evidence of those qualities and find a place for her based on them, they would probably have a wonderful working relationship. Here is where the recommender casts her spell.