How do I help my SO get over her insecurities with sex?

So I've been a very good friend with this girl, 21, for about 9 months now and we decided to give dating a try after she semi-recently broke it off with her boyfriend. Thing is, we are now absolutely in love but she is terrified of sex.

She readily admits she is horny as hell and wants to do it, but due to how her last relationship ended, her BF basically refused sex for the last few weeks, she worries she isn't "good enough" or experienced enough or some shit like that. I'm happy to give her time but Jesus Christ I have no clue what to say or do to help her not panic everytime we start going towards sex. Any ideas on helping her just be comfortable with herself again?

Also I'm happy to provide more details if any of this doesn't quite make sense.