144 hour visa free transit (urgent)

My aunt (holding an american passport) has mistakenly purchased the roundtrip air ticket hong kong-shanghai to qualify this 144 hour free transit.

since she has plan to visit taipei after shanghai, can she simply buy an additional single ticket from shanghai to taipei in order to qualify for this free transit policy?

which means she uses her roundtrip ticket from hong kong to shanghai, show to the customs in shanghai of her additional single ticket from shanghai to taipei, dispose her return shanghai to hong kong ticket.

pls reply asap, possible by noon today, since she is leaving in 2 days.if it works, she will purchase her single ticket from shamghai to taipei immediately