A woman who drowned her three-year-old daughter in the bath to prevent her from having contact with her estranged husband has been found guilty of murder.

Claire Colebourn, a former biology teacher, said she drowned her daughter Bethan because she believed she would be “safer in heaven” than with her husband, Michael.

Colebourn, 36, also wrongly suspected he was having an affair with a work colleague at the marine company of which he is chief executive, a court was told.

Bethan was murdered at the family home in Fordingbridge, Hampshire, in October 2017.

After drowning Bethan, Colebourn, who has diabetes, tried to kill herself.

Colebourn denied murder but was convicted by a jury at Winchester crown court. She did not react as the verdict was returned and will be sentenced on Monday.

In the witness box, Colebourn claimed her husband “hammered” her emotionally and would not let her and Bethan “be at peace”.

She wept as she told the jury she thought the only way to keep her daughter safe was to kill her and ensure she could not be anywhere near her father.

“When your emotions are being hammered by somebody so much and you see your beautiful little girl suffering as well because she feels for her mummy,” she told jurors.

“She’s going to be a lot safer in heaven than she is anywhere near her father. The spirit can be at peace then, and Michael would not let us be in peace. I would walk to the end of the earth for her.”

When asked by the prosecuting barrister, Kerry Maylin, what she had intended to do to Bethan in the bath, Colebourn said: “I can’t use the words you want me to. She was going to be safe, because she would be in heaven. Bethan was going to pass into heaven.”

Before the murder, Colebourn researched drowning on the internet and looked for information on churches and cemeteries. Bethan’s body was found the next day in a downstairs bed, her hair still wet.

Confessing to police, Colebourn said Bethan told her she did not want a bath. “She went to the bathroom, saw the bath running and just said: ‘I don’t want a bath mummy, I don’t want a bath,’” she said.

“I have never been so stressed in my life. Then I drowned my daughter; I drowned my own daughter. It’s going to haunt me for the rest of my life. Her whole body jumped after holding her for a while.

“She didn’t fight against my hand. Her arms were tucked under her. I think sadly, very sadly for her now. She had complete and utter trust in me, didn’t she?”

In his closing speech, Karim Khalil, defending, described his client as “a woman in emotional turmoil”. He added: “This is not a case where we say this lady is innocent. But we say she should not be described as a murderer.

“Whatever your verdict, she will receive a very significant prison sentence. But that will not be the real sentence. It is that for however long she remains alive, she will wrestle with, try to understand and grieve over that she did it.”

In the UK, Samaritans can be contacted on 116 123 or email jo@samaritans.org. In the US, the National Suicide Prevention Lifeline is 1-800-273-8255. In Australia, the crisis support service Lifeline is 13 11 14. Other international suicide helplines can be found at www.befrienders.org.