How does "The Deadliest Woman in the Galaxy" get apprehended in prison?

Question

So Gamora is "The Deadliest Woman in the Galaxy" How is it that just a few inmates(3 to be exact) were able to apprehend her to kill her in prison? It seems very easy for someone who is so skilled in the arts of fighting?

The same night, Gamora was dragged out of her cell by Moloka Dar and a team of angry prisoners who wished to murder her. She found herself being saved by one of the inmates, Drax, whose wife and family had been murdered by Ronan. Drax explained that he wished to kill Gamora himself in order to briefly satisfy his hatred, but was stopped by Quill, who arrived and convinced Drax that he needed her to get to Ronan. While initially distrustful of each other, Gamora offered to split Tivan's payment with Quill, Rocket, and Groot if they assisted her in escaping from the prison.

Answer 1

It's perhaps not entirely clear in the film, but the Junior novelisation makes it abundantly clear that Gamora (having basically done a heel-face turn) is resisting the urge to kill her attackers, even if that ultimately means her own death. She sympathises with them and is doing her best to make amends, starting with not murdering them. On top of that, she's just plain outnumbered by a "team" of hardened criminals who were substantially larger and stronger than she was:

Peter looked at Gamora, seeing that she had heard everything Rocket said. “It’s okay,” she told him, a sad look on her face. “Whatever nightmares my future holds shall be dreams compared to my past.”

...

That night, as Peter tried to fall asleep, he heard the sounds of a struggle in the hallway. When he went to the door, he witnessed a large, muscular, green-skinned prisoner with red battle tattoos dragging Gamora, kicking and fighting, down the corridor.

...

“Ronan murdered my family,” growled the man, anger boiling behind his words. “On that day, every cell in my body united in the single purpose of one day destroying the man who was responsible. Because your master, Ronan, took them from me, I will now take you from him.”

Gamora rushed to explain. “I, too, despise Ronan. And my so-called ‘father,’ Thanos. I have tried my whole life to escape from their grasp. The only reason I’m here is because I finally had an opportunity to be free.”

Answer 2

TL;DR - A guard was behind the attack, plus she goes willingly to bide her time.

---

We never see the actual abduction on-screen - when the scene begins, there are already six prisoners present (well, five prisoners, one guard), with one holding a knife to Gamora's throat. Although she does show anger when they announce their intention to kill her in the shower room, she does not struggle much and allows herself to be taken there. Keep in mind that, at this point in her life, she is attempting to "turn over a new leaf" and stop being an assassin. This likely means that she was hoping to talk the prisoners out of it, then escape if that didn't work.

Once Drax enters the picture with a clear intent to kill her, she easily disarms her captors within seconds. This leads us to believe that she could indeed have done so earlier, but chose not to.

As for HOW they actually got the drop on her, she was most likely asleep given that the other prisoners are shown sleeping. Even the deadliest person in the world... er, galaxy... can be caught by surprise on occasion. It's how they react to that surprise that defines their skill.

Also, note that the attacker giving the orders is wearing a guard uniform, and is most likely a corrupt guard (with all the access that would entail). This explains how the prisoners were able to get into her cell in the middle of the night.