China Travel Document Question

I would like to buy tickets for my family, but one of my daughters has a travel document (luxingzheng). She was born in China to one Chinese National parent (at the time) and one Canadian parent. Even though she has a Canadian passport, China considers her Chinese and she was issued a travel document. She will be entering China using the travel document. I cannot see an option to choose luxingzheng (travel document) because she's not from Taiwan/Macau/Hong Kong. Could you please let me know how I can choose this option to buy train tickets? Thank you!