dogs timid behavior at dog park

Question
We just brought home a 1year old terrier mix, 12 lbs. from a rescue shelter. Her name is Blondie. We don't know her background. My son brought over his 5 month old terrier and they got along great playing together. When we have taken her to the dog park she stays 99% of the time right next to us and puts her tail between her legs when other little dogs approach her. We've been to the small dogs only side 3 times now and she hasn't seemed to warm up to interacting with the others. We walk around and she just follows us even when we walk over to other dogs who are interacting. Please give us some ideas. We've also thrown a toy ring which she will fetch somtimes but if another dog is near her with the toy she backs away and lets another dog pick up the toy.  We want her to have interaction with others. Each of the 3 times we have gone it has been for at least an hour. Thank you in advance for any help you can offer.

Answer
Hi Robin,

The hardest part to working with you to help Blondie's is that there is no history, except that she came from a rescue shelter. Based on your writing, I have to assume that there was at least one unpleasant experience she suffered while at the shelter.
Your son's puppy, being at least 6 months younger than Blondie, posed no threat to her and, her realizing this, allowed her to befriend him without hesitation.
Her tail between her legs is a sign of her being anxious/fear at an approaching dog. The good news is that she is not aggressive to them when they approach. She will hang close to you as you are her protector.
I wish there was an easy solution to your problem. Unfortunately there is not. However, I highly recommend you enroll Blondie first in an on-leash obedience course. Incorporate that with an off-lead obedience program once she successfully graduates from the basic course. The trainer will guide you in all steps.
I suggest an on-lead basic obedience course in order for you to develop a form of control with Blondie. I am not primarily speaking of the exercises she will learn, I am more concerned with the discipline she will receive and the confidence that she will build within herself. Once you move to the off-leash program, there will be exercises where you will leave Blondie a distance with other dogs close by while you leave her. i.e. Perhaps you will command her to sit and stay having a dog on either side of her and close to her. You, by leaving her twelve feet and more, will begin to help her build more confidence around other dogs, and--more important, help her to break the separation issue when you are with her.
It is a lengthy process, but I am confident that you can reach your goal. This is a situation, at this point, that is correctable. It will just take time and patience.
I wish you the best of luck. Please advise me as to your progress as time goes on. I am interested.
Harry