My dog is a lover, not a fighter

I went to the dog park today. It's a great way to take care of the energizer bunny that is Coco. She eagerly jumps out of the car (the same car that she crawls into with a lot of verbal cues and a mod assist - aka she gets a lift). Coco and I get past the safety gate, I let her off her leash and she runs. There are three other doggies and she plays with them for 5 minutes. Sadly they're leaving so it's just us in the big dog park. A little bit later, a lady with 3 little dogs moves over from the small dog park into the big dog park. She carries the little one and the 2 jack russels run around. The lady starts chatting with me and one of the little dogs comes over to Coco.

And then the jack russel starts attacking my baby girl.

The lady yells at her dog. Poor Coco has her tail between her legs, the hair on her back raised and she's sitting behind me.  I call her and she presses up against me and doesn't move. We walk away and she calms down. They play in their separate areas and then a poodle arrives. Coco, the social butterly that she is, must greet this new friend. The other dog sees Coco running to the gate and goes after her again. I separate them vocally and get to Coco. She had a mustard colored substance on her back. My poor girl!!! She cowered again and then we went on a walk with the poodle. She played in the back area with a beagle and the poodle some and then we decided to go.

Coco is a 70 pound dog and the jack russel might have been 20. But truth be told, my dog is a lover, not a fighter and she's safely home without any bites but without her big girl pride.