Singh, who was considered to be one of the closest aides of Irani, was shot dead last night.
She also took a veiled dig at Congress president Rahul Gandhi for his "congratulatory message."
"On May 23, I got a political message publicly-- Amethi ko pyar se sambhalna (please take care of Amethi with love). I want to tell the person who sent this message that I have received the message loud and clear," she said.
Praising Singh's efforts for the development of Amethi, she said, "I want to say that since 1977, Surendra Singh was living his life as an active worker and a leader who provided solutions to the people on issues of development. Unfortunately today, he has been killed after celebrating victory."
"A saddened BJP family salutes the bereaved soul. The family of 11 crore workers of BJP is standing with his family in this hour of grief," she said.
Smriti asserted that it has been the policy of Narendra Modi and Yogi Adityanath government that justice has to be done as per the law.
"BJP workers and people of Amethi can be sure that his killer will be found out even from beneath the earth. We will get justice for Surendra Singh's family," Smriti said.
She also urged BJP workers to act with restraint while warning that this killing was an attempt to "terrorise" Amethi.
"I request BJP workers to show restraint. Surendra Singh was killed to divide and terrorise Amethi. The development will reach every household of Amethi in his (Surendra Singh's) memory," she said.
Earlier, Irani met Singh's family and even lent a shoulder to the mortal remains of her deceased aide.
Seven persons have been detained for questioning in connection with the killing, police said, not ruling out political rivalry as a possible motive.