You can be both jealous and trusting at the same time, it depends on how you handle the jealousy and not let it get out of hand. A little jealousy is actually healthy in a relationship, it lets you know that you're being loved and wanted, and yet there is still a lot of trust there.
My strategy was to reassure her b.f first, so that he wouldn't jump up and be all angry at her for being so insecure, possessive, etc. Even though she might feel really really jealous - the unhealthy kind, she still can't show it, or the relationship might go in the wrong direction. She still has to be logical and know what she should do and what she should say, even if it isn't what she really feels - I find that this is really essential at times, that you can't tell a guy how you really feel, if it is destructive. If she can manage to let him know that she's only 'healthily jealous' and that there is still trust in existence, then it'll all be good. Try to imagine that a guy isn't jealous at all...and doesn't care how the girl go about treating other guys, no matter how closely, would that make her feel 'wanted' in the relationship?! Oh wells, hope it all goes well with Bonamy.