If you buy her.. or ANY animal in a petstore that takes such horrible care of their animals, you will not be "rescueing" her. You will be Buying her, which will encourage the owners to get more, and keep them in exactly the same conditions. Maybe try talking to the owner and giving them a Care sheet to see if he will change some of the conditions. Try the ploy of "You know, if she looked healthier, I know a few people who would LOVE to buy her. Too bad." Maybe if he thinks by keeping them in good conditions he can sell more, he would up the conditions, not as if it is all that hard to keep a BP properly.
In the meantime yes I would contact any Animal Welfare organizations possible to report the store.
Wolfy