I think it’s worth noting and even respecting just how much punishment Jasper can take.
When we last saw her, she was thrown into the reactor core of a spaceship, which then crashed, and pulled herself out of the rubble without needing to regenerate.
In the latest episode, we see that Lapis is still keeping her imprisoned, but it’s taking everything she has to keep Jasper down. Her complete, undivided concentration AND the entire weight of the ocean is what’s keeping Jasper from escaping.
Good god, that level of fortitude is insane.