Although Shao Cheng has spoken about rescuing the older woman a moment ago but it didn't mean that he will take her out now, after all, he needed to absolutely clean up the entire Ma Family first without leaving any evidence or single clue regarding his dealing with them.
Meaning, Dai, Dalle, and Mrs. Suyin's relationship with the Ma Family is needed to be completely cut off so that in the future, no one will be able to recognize, figure out and make a connection to Shao Cheng operations against the Ma Family if someone has noticed the three people working his side.
Aside from the Ma Family targeting his older brother Yan, Shao Cheng wouldn't leave a clue about having different affiliations with that Family in the future.