Socializing a big, scared puppy

I got my pup, Nixie, about five and a half weeks ago. She's about seven months old now, and is a terrific, fantastic dog. She's a Border Collie/Australian Shepherd mix who's very bright and surprisingly mellow for such a mix of breeds. She's medium-large, weighing about 40 pounds. When I got her, she was spending most of her time in an outdoor kennel with one of her more dominant littermates, had received little to no training, didn't get to meet very many people, and was not housebroken.

Since then, I've taught her many basic (and some not-so-basic) commands, gotten her used to walking calmly on a leash and reliably able to be off-leash playing fetch at the park, and housebroken her via crate training. She's obedient and eager to please. She used to act somewhat aggressive towards my cat, Abby, but through gradual introductions, she now likes her (although Abby still doesn't like her!).

Nixie's weak point is that she's very, very nervous around other people and takes a very long time to warm up to them, if she does at all. I take her in to Petsmart regularly, but she acts very skittish when other people get near her. She's a good girl and has never growled or bared her teeth at anyone, but today while at the vet, she snapped at the tech who was about to give her a shot. I had to hold her head and reassure her while she got the shot. No harm, no foul, but it got me thinking that I really need to socialize her and get her more comfortable with people.

Furthermore, she's either standoffish or even slightly aggressive towards other dogs. She didn't care about my parents' dog (she literally didn't even acknowledge her), but with certain dogs, she bristles and growls and stands very close to me. Other times, she just tries to avoid them. She's a wonderful dog, but it's plain that she didn't receive the kind of socialization she needed in her formative months.

I'm not really too hung up on having a really social dog--she's special whether or not she enjoys the company of other people or dogs--but I don't want her fear-biting a well-intended stranger (or friend!), be they human or dog. What are some safe ways I can go about socializing her? I want her to get comfortable with other dogs and people, but in a way which won't put her or others at any kind of dangerous risk!

Let her have some time watching people and other dogs at a comfortable distance. When she is calm, reinforce that behavior with treats, stroking, whatever seems to make her happy and relaxed.

As she gets more comfortable, reduce the distances.

Recruit friends she's not familiar with to start meeting her and reinforcing that people = good things. Let them offer her a favorite treat, but be sure they understand to let HER come to THEM and don't crowd her. I'd also suggest you start this in a neutral, outdoor setting so she won't feel like she has nowhere to go and she also won't feel like her space is being compromised.

Anything you can do to bolster her self-confidence is going to be gold. Work on simple obedience exercises or tricks with her, even something as simple as praising her lavishly when she catches a ball or brings you a toy will help. Anything she does right, tell her. A confident dog is a stable dog.

You might also look into T-touch therapy. You can learn to do it yourself and it can really help in many instances.

Thanks for the advice, Renee! I'll look into T-touch therapy and see if any of my friends want to come and help her overcome her fear of strangers

She sounds a bit like my dog. I work with him when I'm home and he improves, but when I go to school training stops and he does regress some. I see the biggest improvements when I can get him into a pet store at least twice a week. Now not all shy dogs are ready for pet stores, some would be having a panic attack the entire time. You'll have to decide whether or not the trip would be too stressful for your dog.
I know the first time I brought Tucker to the pet store we stayed away from people because he needed to get used to the store itself, he was too jumpy to add people to the mix. So we found deserted aisles and walked up and down, letting him sniff. I brought food and we practiced some obedience. Eventually he'd venture to the ends of the aisles to peek out at people, as they came close to the aisle he'd retreat. if he chose to bark instead I'd walk him back into the aisle, encouraging him to come with me. We did this for a good part of the visit. However he got comfortable enough to simply lie down in the aisle so I moved so an aisle by the entrance so he could watch people walk by, but still be able to retreat down the aisle if he got scared. He is actually very curious and would get closer to the door so long as the people ignored his existence.

Anyways we kept working up like this, first by letting him watch and telling people they could not pet him. Now he will take treats from most adults but will not allow them to touch him, we'll keep working. It's all about going slow, at the dog's pace.

^^^^^ that is great advice. Allowing the dog time, allowing some distance, showing that their ok, and they are not being forced before the dog is ready. Exactly what I would do.

I would do this under supervision of a dog behaviourist if you are worried that she might snap at other dogs or people. It's a good investment.