The knights tackled him, but he was still able to escape from them fast enough and literally bumped into Shrek.
Shrek scared the knights away by posing as the giant, and after that, Donkey wanted to be Shrek's friend to repay him.
She flirts with him persistently, even though Donkey doesn't show interest, it doesn't stop her.
This description fits Donkey himself, and the name "Gabby" possibly could be "Donkey".
When they meet him, Farquaad decided that in order for the fairy tale creatures to leave Shrek's swamp, they must rescue a princess (Fiona). While Shrek is looking for the princess, Donkey gets chased by a dragon who cornered him on a broken bridge.
As the dragon was about to eat him, he smooth-talked her so he would not be eaten, but she fell in love with him and took him to her chambers, shaking her hips back and forth happily as she carries him away.
Donkey pleaded to stay, but Shrek kicked him out, so Donkey stayed outside.
Then, at night, Shrek found many other fairy tale creatures outside his house (besides Donkey).