This is my theory as to where Jemma was transported by the monolith.
First off what or who is Ego?
Ego is literally a living planet. Created as other planets were except that as he once told the Asgardian Prince Thor, he was a scientist that merged with a planet.
Ego has complete control over his surface down to the molecular level. So much so that he regularly shapes the surface into a giant face to help communicate with other beings.
His powers include a vast variety of psionic powers. Which lets him read minds and cause a psychotic break downs of his victims.
This is where Jemma and AoS comes in (Spoilers)
The most recent episode entitled "4,722 Hours" in which it shows Jemmas' time she was gone after being transported by the monolith.
While on a mysterious planet she meets a man named Will, who wound up on the planet after he and a team were sent into space by NASA in 2001. He recounts his tale to Jemma about how the rest of his team met their fates. He tells her that they all went crazy and either killed themselves or attacked him and he was forced to protect himself and end their lives. He also tells her that the planet attacks.
We also learn that while trying to escape he tells her of a chasm that is only 30 meters across but when they get there it has expanded and he remarks "It(the planet) doesn't want us to leave."
So a planet that appears to be alive, can shape its surface at will, and causes people to go crazy, Tell me how that doesn't sound like the living planet Ego!
Tell me your thoughts in the comments.