Anita Turner, 51, told Winchester Crown Court her son Elliot did not kill Longley, 17, in his bedroom at their Bournemouth home.
And she denied perverting the course of justice – a charge that Elliot, 20, admits.
Longley was found strangled in Elliot’s bed on the morning of May 7.
Indonesian-born Anita told the court that on the morning of the discovery, her son woke her up and asked her to wake Emily.
“I called her name. Emily was asleep with the duvet [on her]. She didn’t wake up so I just tapped on the duvet. I called: ‘Emily, Emily, wake up, wake up’,” Anita told the court.
“She didn’t wake up. I didn’t think anything at all. I made a cup of tea and I still called her.
“I tried to let her sip the tea but her mouth would not move.
“I called Elliot and we were both trying to wake her – we kept shaking her.
“I said: ‘There is something really wrong – she does not move’.”
When asked why she did not call an ambulance, Anita replied that she did not at that point know Emily was dead.
She also denied helping to destroy a letter that the prosecution alleges was a confession to the crime written by her son.
The trial continues.