The mother of a brain-injured girl told a St. John's trial Tuesday that her daughter was healthy and happy shortly before she was allegedly shaken by her father.

Meanwhile, court was presented Tuesday with the transcription of an emotionally raw texting exchange between Kate Coombs and Colin Matchim, who is being tried for aggravated assault in the alleged March 2009 shaking of their daughter, August.

Colin Matchim is standing trial for allegedly assaulting his baby daughter. CBC

Kate Coombs told Supreme Court of Newfoundland and Labrador that she changed and washed her daughter, and then left the infant with Matchim because she had to go to the bank.

Court has been told the girl, who was three and a half months old at the time, has significant neurological damage.

Coombs testified that when she returned home, August was grey, pale and cold. The baby was taken immediately to the Janeway children's hospital in St. John's.

Coombs said she fainted when she was told that the baby was brain-injured.

The transcript presented to the court shows the powerful emotions between the then-estranged couple in the days immediately following that incident.

"I cant [sic] live without you," Matchim texted Coombs, who had gone to stay with her mother and had told Matchim she wanted no contact with him. [Read the full transcript of the exchange here.]

"i am not trying to be a bitch but i can;t talk to you knowing that something happend to baby August when i wasn't home and you can't tell me what happened," Coombs texted to Matchim.

"i know but im going insane," he replied.

The texting exchange happened just before Matchim confessed to police that he had shaken his daughter, but had not intended to hurt her. The defence has said Matchim made the confession only because he felt threatened by a social worker, who said he would otherwise lose access to his child.

After Matchim told her that he was scared, Coombs texted back, "your scared, you know if i loose August im going to have a nervous break down."

"i know me too," Matchim wrote. "i'm having thoughts. i just can't deal with this anymore."

Later, after telling Coombs that he was afraid she would "disappear out of my life," Matchim agreed to speak to police once more.

"just know that it was an accident ok she was holding her breath and she wouldnt let go and i panniked."

Coombs stopped engaging with Matchim, who repeatedly asked for her attention, at one point typing Kate!, with dozens of extra exclamation points.

Coombs, who made a copy of the texting exchange after Matchim requested she do so, testified that she was too angry to respond to Matchim.