Doesn't she have a phone (didn't watch the whole video)? Even if not she could ask her customers to show her the tx details on their phones (right after payment is made).
Don't really see a problem here. There's always some risk of double-spend attempt if she doesn't wait for confirmation, but I don't think anyone would try that for such small value service.
There's probably much higher risk of someone simply refusing to pay and walking/running away.
It would not be totally unexpected for a tx to take a minute or so for it to propagate throughout the network, so her customer could say that they paid her, wait for her to say that she can't see it on her end and then either actually send the tx if she says she can't see it, or not send it at all if she says that she can (because she has not wireless access)