Ok, here is the deal:
Pausanias is our chief primary source on the Sibyl of Cumae. Frazer made a famous translation of Pausanias.
I have not read Frazer's translation. I have not read Pausanius word for word either, only passages and summaries.
However, the only thing in summary I can find is this: Pausanias mentions the locals at Cumae showed him an urn. The legend was the bones of the Sibyl were stored therein. Apparently the myth was the Siby asked her patron god Apollo to live for a thousand years, but she did not ask for the youth to go along with it; so after a few centuries of aging she becomes a very shrivelled up creature that can fit inside a jar. Pausanias apparently wasn't impressed by this colorful bit of local folklore.
My advice is, if you are so inclined, find a translation of Pausanias by someone other than Frazer and read it yourself word for word.