Emma,
I would wait for a day or two before doing anything. The holidays are hectic, but if she doesn't respond to the first round of trying to contact her (I would send an e-mail to the address provided on the purchase receipt as well as sending a convo on here)....I would send her another round of convos to let her know that if you don't receive payment you will need to cancel the transaction.
Edit: I also thought about the fact that Paypal has hiccups sometimes...so maybe she will send another one through, or it might take a day or two for it to register in your account since it is an e-check.