About fifteen minutes after I posted this thread, Sally passed.

We called the vet to inform her of this and she said that sometimes pet stores guinea pigs (and also other animals) carry diseases that cannot been seen or known until it's too late. She thinks this was the case for Sally. Even though we only had her for a couple months, it breaks my heart that she's gone.

This afternoon we plan to bury her in our garden. RIP Sally.