Maybe she had a ticket that covered her journey as far as Theale. I often use my season ticket and travel beyond its validity - and then have to buy on board as the ticket machine at Nailsea will only sell tickets valid from that station. If the TM reaches me before the break point then I show the season and ask for a ticket for the balance, but if they reach me past the point of validity I just ask for a ticket from X.
From what I saw of her 3 section YP card holder - one had the YP card, one had her photo and blank for section 3.
But to be honest TM's rarely check the carriage - they coach spot checks on the way to Reading. After Reading no check is performed. I am surprised they even have time to check between Theale and Reading