We don't know if Kaylee received her degree at the December Commencement Ceremony at U of Idaho, we just know that her name wasn't in the program among those graduating. There was some pushback about this in the media at the time. Some people felt that the University omitted her name from the list of graduates so as not to detract from this significant occasion for the students and families who would be present. Not that they did that, but that's what some people believed. Maybe her family, for some reason, didn't want her name to appear in the program, although I think that is unlikely, JMO.
If she had met all the degree requirements and was set to graduate in December, then I think her family would have already received her diploma on behalf of Kaylee. Usually students receive their actual diplomas a month or so after they graduate, not at the Commencement Ceremony itself, even though they are handed something as they cross the stage and shake hands with their dean or university president, etc. (however that particular university organizes their ceremony). The actual diplomas are provided at a later date.
If Kaylee still had work to turn in and had not officially completed the requirements for her degree, then a posthumous degree would be awarded, usually this requires formal approval by the Board with a vote taken at a scheduled meeting of the Board. So if Kaylee didn't receive her degree following the December Commencement ceremony by way of her family receiving it on her behalf, then I would think she would be awarded the degree posthumously at the May 2023 ceremony, if that is what the family want and the Board approves it (which of course they will, she had completed most of her degree requirements, if not all).
At the university where I work, posthumous degrees may be awarded if the deceased student has completed a certain percentage of their degree requirements and they were in good standing at the time of death - and if the Board approves it formally when they meet, and the degree is awarded at the next commencement ceremony following Board approval. We usually have at least one student (an undergraduate or graduate student) per semester receiving a posthumous degree -usually because of terminal illness, accident, or suicide. It's always a very sad occasion, but very meaningful, of course, for the family.