A teenager accused of the attempted murder of two teenagers and a pupil woke in a “bad mood” on the day of the attacks, a court heard.

The unnamed girl, 14, is said to have pulled out her father’s fishing knife when she was challenged over wearing non-school uniform trousers and told to leave the school hall. Swansea Crown Court was told she yelled “I’m going to f***ing kill you” and then stabbed deputy head Fiona Elias, 48, as well as special needs teacher Liz Hopkins, 53, and a 14-year-old pupil.

The girl has admitted three charges of wounding with intent to cause grievous bodily harm and possessing a bladed article but denies attempted murder. She told the court: “I get very upset or grumpy when I’m on my period. I woke up in a bad mood that morning.”

Giving evidence, the girl added she had armed herself with a knife in school since Year 3, because she felt “scared and worried”. She said: “I had been carrying all kinds of pocket knives and multi tools since I was in primary school.”

The teenager admitted telling friends she wanted to hurt assistant deputy head teacher Fiona Elias but said: “It was more of a joke, I didn’t want to hurt anyone.” The girl said she thought “beating up a teacher” would get her expelled because she was known for being a troubled individual.

The court heard her father searched her school bag every day after she was caught in possession of a vegetable knife in lessons six months earlier and suspended for a week. She managed to smuggle her father’s multi-tool fishing knife into the 1,500-pupil Amman Valley School in Ammanford, Carmarthenshire, on April 24 – the day of the stabbings.

Mrs Elias received wounds to her arms and special needs teacher Mrs Hopkin was stabbed in the neck and back when she tried to intervene. The girl went to another part of the school grounds to carry out the attack on the 14-year-old pupil who she “didn’t like”. All three were home from hospital the next day.

The court heard how, in the back of a police van, she told officers: “I’m pretty sure this is going to be on the news so more eyes will be looking at me. That’s one way to be a celebrity.”

The jury has heard that when the girl asked police if they knew the injured pupils she said: “I stabbed her, oopsies”. In court the girl said she felt “sick ” and “terrible” as she sat in the police van with an air ambulance hovering overhead.

Caroline Rees KC, defending, asked how the girl felt now. She replied: “I feel terrible, guilty. I regret the way I behave, I feel sorry, I’d do anything to go back.”

She said she didn’t attempt to murder any of the three victims and didn’t want any of them dead, adding: “I remember thinking to myself: “What am I doing? Stop. I can’t look back, it’s dark, I remember being very hot.”

The trial continues.