Hey, and welcome! I'm pretty new myself, but from the research I've done I'd say you want to quarantine her in a smaller 6qt tub before introducing her into her new permanent home. I wouldn't really rely on PetSmart having taken the best care of her given her hatch date being in Dec. 2015 and only at 140gI'd say they were definitely lying about her feeding pattern or feeding her incorrect sized prey.
You should post some pics of her when you get the chance. As for food, did they feed live or f/t? For her size, she should eat rat fuzzies or small mice. Generally about 10-15% of the snake's body weight. You'd want to get to rats first though since they can be picky eaters and rats are easier in the long run in terms of how big of a prey you'll feed when she's full grown.
Oh and you should probably leave what your enclosure is like, heating temps, what the humidity is, etc. So everyone here can have an idea about your set up and if it's suitable for your little noodle. More people can help you understand why your snake is acting a certain way, or why it won't eat, etc.
I'm glad you're committed to your animals! I'm hoping she grows to the ideal weight soon. Update us on her health and congrats with your noodle baby!
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