If she wasn't socialize properly as a very young puppy, then yes, it's perfectly normal. The window for socialization closes at 16 weeks. After that it's a very difficult, long, slow process. If something scared her then, if she wasn't exposed to tons of stuff, if she was abused, then her reaction is normal. Also, if her mother had a timid temperment, it's normal and even harder to overcome than lack of socialization. I have three dogs here who are genetically shy. They've come a long way, but they will never be brave, outgoing dogs.