I want to know how Islam deals with masturbation. I have a friend that sometimes cannot stand it and she starts masturbating and when I am angry with her, she asked is it better to have sex with man and make Zina? What do you think about that? I need an answer because these days she looks so depressed because I told her, you will never be forgiven and that your prayers and fasting are nothing.

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

As for Shari'a ruling concerning masturbation, please consult our Fatwa: 81167.
As for your saying to your friend that her prayer and fast are not accepted and her sin will not be forgiven, we state that you are completely wrong. In addition, maybe Allah will punish you for making people lose hope in His Mercy. Furthermore, such a behavior of yours may undermine good work and incur Allah's wrath, since Allah's Messenger (Sallallahu Alaihi wa Sallam) said: "A man said, By Allah! Allah will not forgive the sins of so and so; Allah has said: Who is he who took an oath that I (Allah) will not pardon so and so? (Know that) I have pardoned him and undermined your work" . [Reported by Imam Muslim ].
Maybe you said the above-mentioned words as a form of desire and vigilant concern to help her to avoid violating Allah's prohibitions. If the matter is so, then that is good Insha Allah; otherwise, it is not good.
Anyway, you have to advise her with kindness and mildness, to remind her of acquiring useful knowledge and taking good friends, to make Du'a in abundance, and then, to pray to Allah to grant her a good husband who helps her to do good her the present life and for the Hereafter.
We pray to Allah to set our situations right and to purify our hearts.
Allah knows best.