My 21M GF 21F has trouble rejecting a guy.

So my GF and I have been in a relationship for a year and she went to the US to work as a lifeguard for summer. Right now she’s a trainee and a guy around her age hit on her and on her break she instantly called me telling me she feels awkward and that he brushes him off but he just insists. She has told him that she’s in a relationship but he just keep trying throughout the day, when I tell her why she doesn’t straight up tell him that’s he’s not interested she told me that she’s scared that he’s gonna badmouth her to the examiners because he’s a close friend with one of them. I try to be supportive but it just hits me in a weird place that she’s doesn’t straight up reject him, although I know she’s incredibly shy and a huge people pleaser. What can I do to ease myself and comfort her and overall handle this situation?