The Pennsylvania mom accused of killing her husband and their 3-year-old son at a Poconos resort showed no signs of trouble in a video call just hours before the attempted murder-suicide, according to her stepmom — who now believes she had planned it for weeks.

Metallica Rose Harrison, 27, had never shown signs of mental illness and appeared normal in a video call Sunday, the day she allegedly stabbed her husband and son and tried to slit her own wrists and neck, her stepmom April Thetga told The Post.

“She had called and we’re video chatting, and then she says she loved us very much, just like she normally would,” Thetga recalled.

“It wasn’t an odd conversation,” she said.

“It was a loving family. We’re just as shocked as everybody else.”

Harrison’s family found it “odd” that the mom and her husband, Chris, were having an extended stay at the Great Wolf Lodge, but assumed it was because their “amazing” and “very happy” son Tristan loved playing in water parks so much.

But after the murders, they were shocked to find out that the murder weapon was from a set of knives Metallica had brought from home, the stepmom revealed.

“I was told the knives came from her home. Her house. So to me, it was planned,” Thetga told The Post.

A butcher knife was found on the bathroom floor and a smaller knife in the bathroom sink, according to the police.

As for the motive, Thetga said relatives are completely in the dark.

“We’re just as shocked as everybody else. … We want answers,” the stepmom said.

“They were always happy. This is devastating.”