Low self-esteem. It's not mutually exclusive to either sex.
And, mirroring this low self-esteem happens as well. We ALL have insecurities within us. These insecurities are just waiting to pop out at inconvenient times. However, you can't be worried about this happening. You have to stay in the moment and not live in that fear. Just realize the insecurities are there. Honestly, you should know your insecurities anyway and work on them. Anyway, these things tend to mirror the same insecurities in other people.
When us as guys are handling women that have insecurities, it tends to get frustrating. However, flip that around . . . if you have insecurities, it likely gets frustrating for her as well. Just realize, even a QUALITY girl will have insecurities, somewhere. Understand that. It's human nature. Don't knock her for it. Understand it. Help her move past it