You cannot make her feel secure - or make her feel anything else. You can have input on some of her circumstances, but how she relates them to certain feelings is entirely up to her. The best you can do in this situation is to provide her with the opportunity and give her reason to feel secure with you. If, when you're out together, you're ogling other wimmen, then that's probably not a good thing. But my sense is that her issue has more to do with what happened to her long before you were in the picture.
Best advice: As in all things, be yourself.