Just for laughs, Grindelwald rigged Graves up so that whenever someone entered his prison Graves would fall and be hanged unless a counter spell was cast in advance.

Tina doesn't know. She comes to the rescue, only to watch Graves get killed right in front of her.

Less angsty option:
He falls, but she's able to slow his descent so the noose causes less damage. He's strangled, possibly has a broken neck, but survives.