Welcome! Great questions. I have been doing some digging and so far I have only been able to find some information on a reddit posting about possible there being 2 people that were four wheeling where her car was found. I did see somewhere else that there was a mention of a possible ex but no details. It seems like nothing else is mention except what we have listed on the page at the moment.
https://www.reddit.com/r/coldcases/comments/zpfrjw/anyone_ever_hear_of_the_amber_berbiglia_age_23/
https://www.reddit.com/r/UnresolvedMysteries/comments/tv02kf/who_murdered_amber_berbiglia/