Can I still help my unsocialized older adopted dog? Is it too late?

Poor Mia! You're right that a lack of proper socialization as a puppy can cause adult dogs to be quite fearful and sometimes reactive or aggressive towards strangers or new things. Technically speaking, you can't really "socialize her" anymore at this age - the socialization period in dogs ends at about 16 weeks of age. After that, the brain changes and is no longer as receptive to new experiences.

This doesn't mean that there is nothing you can do to help her, but it does mean that it will take much more time and effort than it would have if she were still a young puppy. Normally, the general approach for this problem is to identify what types of situations are scary and stressful for her, and help her to associate good things with these situations by feeding her treats or playing a game she enjoys. It's very important to go slowly and make sure that she is comfortable every step of the way - if she's anxious or afraid, then this is making things worse instead of better.

Because it can be very difficult to work with a dog like this successfully on your own if you don't have any dog behavior experience, I would really recommend making an appointment with a veterinary behaviorist or a good reward-based trainer who can evaluate her in person and help you put together a detailed plan to help her become more confident and less afraid. You can search for a board-certified veterinary behaviorist here (www.dacvb.org) or a qualified trainer in your area here (www.ccpdt.org).