Since it's an on-and-off change, and she complains that it feels scratchy, it's quite likely allergies. Acid reflux is a possibility too, if you know she has that problem anyway. If she had a cold recently, this could be a lingering irritation. Much rarer would be a polyp growing in her throat. Voice changes due to maturity are rare in kids so young unless there's an endocrine disorder, and she'd probably have other symptoms as well, like the growth of pubic hair.
If it's really bothersome, I'd check it out. A month would probably be okay to wait if it's only occasional and not troubling her too much.