After that the king says to Molly: 'Molly, you are a clever girl, but if you would do better yet, and steal the giant's ring that he wears on his finger, I will give you my youngest son for yourself.' Molly said she would try. So back she goes to the giant's house, and hides herself below the bed. The giant wasn't long ere he came home, and, after he had eaten a great big supper, he went to his bed, and shortly was snoring loud. Molly crept out and reached over the bed, and got hold of the giant's hand, and she pulled and she pulled until she got off the ring
This is from English fairy tales. I read some English fairy tales and they are usually written in past tense. However there is some sentences written in present tense in this story like "So back she goes to the giant's house and hides herself below the bed". Why does present and past tense mix in this fairly tale?