I was hoping to get some responses back before answering, but I don't want you to go without answers either.
The best way to help a dog become more self confident and less fearful is to start obedience training
them. Then obeying you becomes second nature and as she starts obeying your commands and watching you, she won't be so focused on other people, other dogs and other things that make her anxious.
The following site is helpful in helping owners train their dog. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.
Training works best if you train at least 30 minutes a day (two 15 minute sessions). I would start making your dog work via the Nothing in life is free program (NILF). It is outlined below.
A dap collar which uses pheromones similar to those used by nursing moms to calm her pups is helpful for anxiety situations. They can be purchased at pet stores and online.
IN person group training classes can help with socialization skills and has the added benefit of all the dogs being under the control of their owners with a trainer present to help with socialization.
I also recommend taking it easy when in dog parks. They can actually be detrimental if you run into an aggressive dog. I'd keep socialization at first to situations where the dog does not have to actually interact with children or other dogs but can sit (perhaps on the other side of a fence) and watch other dogs and children while you feed her hot dog slivers if she is acting calm and not afraid. As she becomes more comfortable with that, then you move closer or allow limited interaction perhaps letting other people or kids toss her a treat.
It takes a lot of work and not all fearful dog recover completely but you can usually improve their lives at least a little and there are dogs that do become outgoing and confident.
I hope this information is helpful to you. If you need more information or clarification, please reply and I'll get back to you as soon as possible. If you are satisfied, please take the opportunity to rate.