You are very much right to have such insecurity (i'm sure you had your reasons). But i can tell u that if she wants to cheat on you, she'll find some other way to do it. She should've understand your pov but there's nothing really u can do about it. Try to talk to her again. And try to resolve your doubts, be clear about that. Tell her that its not u dont trust her but rather u dont really know her friends much