My dog can be the same way sometimes. Once the bone is a few days old she's just not interested anymore, even though she's barely made any progress on it. I've found she prefers antlers and will usually chew on them off and on for a long time.
Does Sally do this w all chews? Maybe try something different; something completely edible, but tastier and much healthier than a rawhide, like a Himalayan chew (they're made out of hard yak's cheese) might entice her to keep chewing. See if your parents will let you try a Himalayan chew, they're slightly on the pricey side but if you're just trying one I can't imagine it'd be much of a problem. I'll bet she loves them, most dogs do, she might even chew it til it's gone. I think it's worth a try anyway.
Best of luck.
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