My best friend's struggles with jealousy

Hello everyone! I'm new here (20f), so I apologize if my post is a bit off-topic or not suitable for this thread. I'm seeking advice on how to help my friend navigate her feelings about entering a relationship. Recently, my friend (20f) started developing feelings for a guy she likes (22m). Although they’re not exclusive yet, she’s mentioned that they both want to be. However, she’s been struggling with jealousy issues that seem quite intense, especially considering they haven’t officially started dating. Today, she was really upset to find out that he liked another girl's profile picture on Facebook. For some context, we come from a small town where it’s common for everyone from high school to like each other’s posts, so it was really just a casual interaction. Nevertheless, she’s reacting strongly to this, experiencing anxiety and even losing her appetite. She has a history of being cheated on, and it’s been two years since that happened. I genuinely want to see her happy, but I’m unsure how she can approach this potential relationship with a positive mindset and build trust. I'm reaching out to anyone who has experienced similar feelings of jealousy or has dealt with issues of trust after being cheated on. What strategies or insights have helped you overcome these challenges? Personally, I haven’t faced jealousy to this extent, so I’d appreciate any advice you can share. Thank you for taking the time to read my thoughts! I truly want my friend to find happiness, but I’m worried that something as minor as this could throw her into a downward spiral before the relationship has even begun. Much love to all x