Milly Caller, 22, accepts that she provided a gas that her friend Emma Crossman, 21, used to kill herself, but she denies encouraging or assisting her to commit suicide.
Lincoln Crown Court heard how Ms Caller provided the gas that Ms Crossman used to suffocate herself in January last year in an "act of misguided loyalty".
The accused rejects the charge because she claims she did not think the deceased would actually kill herself.
Prosecutor Mark McKone told the jury the accused was "obsessed and infatuated" by the dead woman and that she would have done "anything for her".
The court was told how Ms Crossman was known to have a history of depression, self-harm and suicide attempts.
"The prosecution accept that some people did not always take her threats seriously," Mr McKone told the court.
The jury was shown Facebook messages between the pair with one showing the accused message Ms Crossman saying: "best friends having final fun day".
In another she said: "I'm losing my best mate. I do understand why you are doing it and I do stand by you but it still hurts. I am sorry."
The trial continues.