It doesn't sounds like she's accusing you to me, I'd send her another message saying you know she's very busy and everything, is there some time you could meet up for a cup of tea? And then you could bring it up, and see what she says. If she had said "When you were cat-sitting, my mom's jewelry went missing" THAT might sound like an accusation. But it sounds to me like maybe that JUSt happened when she sent you the note, so that's what was on her mind at the moment, not that it had anything to do with you, but she needed to vent to a friend.