What is it you're expecting to happen? This is a professional environment still. She has to look great, so it's perhaps not a good idea for you to be there to see what goes on at such a shoot and be unhappy. Then she'll worry you're not feeling okay and that will reflect on camera. Your GF seems communicative about where she's going and what she's doing, there doesn't seem to be an obvious reason for you to get insecure.

Dig a bit deeper into why it itches. Is it her modelling with male guys, if that's the case? Is it the tiny outfits that others will see? She's going to leave you for a lobster? You need a bit more of a clue to be able to work with your worry. A little insecurity is okay, it keeps us sharp. But one has to judge when it becomes a hindrance and gets in the way. This seems to be weighing heavily on your stomach.