Cerys Yemm, 22, was killed by Matthew Williams, 34, in November 2014 at the Sirhowy Arms in Argoed, Caerphilly county.
Williams was Tasered by police and later died.
PC Kelda Griffiths, who was the second officer into the bedroom, said Williams "didn't seem human".
She told the Newport inquest: "It was like something you see on TV, not something you expect to see in real life."
The inquest was told PC Griffiths knew Williams had a history of drug abuse, mental health problems and of previous violence towards the police.
She said she had refused to enter the hostel without back-up.
"I just believed that maybe he had staged an incident because it was so unreal, as that he wanted to get so many police officers there and attack the police," she said.
"It was such an unbelievable, surreal call. He had murdered someone and I have no doubts that he didn't like police and we would have been next - definitely."
Lawyers for Ms Yemm's mother quizzed the officer over the wait to enter the Sirhowy Arms, telling her: "Mrs Yemm is tormented by the idea that your delayed attendance may have resulted in her daughter's death."
But answering questions from Gwent Police's legal team,  she confirmed she had been instructed to meet another Taser-armed officer before entering the hostel, which she said led to a wait of "no more than a minute".
The officer said Ms Yemm was dead when she entered Williams' room - where the killer had already been Tasered.
"As I stepped into the room I recall seeing Cerys's face, which was horrific," said PC Griffiths.
Despite being hit with the stun-gun, PC Griffiths said Williams continued to struggle.
"He was lashing round and banging his head on the floor. There was no stopping him. He had unbelievable strength," she said.
She told the inquest fellow officer Alan Cotterell used his Taser again after urging Williams to calm down.
"Even with four of us there he was lashing around," said PC Griffiths.
She said PC Cotterell fired his Taser into Williams' back or side.
The inquest on Thursday heard another officer say Williams was Tasered "four times".
PC Griffiths said after each time the weapon was used, Williams would stop struggling, but added: "After a few seconds he would start struggling and biting."
She said after the final Taser shot "he did start to go calm", was put in a recovery position and monitored.
"He was breathing," she added.
The inquest continues.
A police officer thought she was going to die as she confronted a "demonic" ex-convict who had brutally murdered a young woman, an inquest has heard.