Or some kind of "futuristic" camera where its strange design follows its strange function
A device that allows one to see certain potentialities, or allows one to view one possible picture of the future at the point it's viewed... She knows when Frigga will die and how, unless that's changed. This upsets Thor, he thinks it's purely Hela/Malekith's doing. With this device AIM/Hydra/Zemo had hoped to finally rule the world by seeing the results of events before they unfold. The design of which she steals from AIM and improves on after the end of Iron Man 3. The technology would fall into Shield's hands completely by the end of CA 2. Mandarin's rings would be a form of ancient technology that AIM can't fully unlock because they can't look into the past, and don't completely believe that Atlantis still exists yet, or that Shield knows about it. Iron Man 3 could do a little more in the way of dropping more Atlantis clues like the spot on the map in IM2 and the Oracle easter egg.
What someone said about a connection to einstein-rosenbridges + the device allowing Jane prior knowledge about the attack, may be right on the money. Einstein believed that time-travel was possible according to some of his theories about time and space; where time is viewed/calculated as mainly an illusion. Einstein even believed that time-travel to the past would eventually be made possible--but only through very particular wormholes. Ones that we'd be able to generate when we actually could generate enough energy to keep a theoretical wormhole open and stable. He believed that by that time we'd understand enough about the nature of time, space, and the universe to build off his theories about time-travel.
Advanced Idea Mechanics (AIM) took great interest in these theories after Einstein and Erskine helped the allies win WW2. AIM and Mandarin would have a deep interest in other cultures/time periods... Particularly those of past rulers, kings, dictators and Emperors. Hawkings even adjusts and builds from Einstein's theories with his view of how time-traveling to the past could be made possible. The common link is the theoretical generation of a wormhole intended to travel one through time, but returns them to the same space in the universe. What Einstein believed you could access with wormholes was a layer of reality so incredibly miniscule that space and time are unable to be separated. Instead, when you get down to that astronomically low sub atomic level you reach a layer where everything exists withing what has been theoretically dubbed space-time... Leading to ideas about the space-time continuum. If Einstein could have a look at all the things he was slightly wrong about regarding the quantum world, then he may have been able to unlock time travel for us. I believe that with the right funding people like Hawkings are closer to cracking time-travel than most realize, at least from a theoretical physics angle. Especially if there is an interplay between light and gravity that we're just beginning to understand. I would insert Hank and Janet as scientists working for AIM/Shield previously on subatomic particles before they discover that looking into space-time through subatomic particles can lead to other effects on the body.
One of the armies in Thor 2 being from other times may be right on the money as well... Furthermore, Selvig may continue to experience things-- to be shown things by the cube. Because of his particular exposure to the cube + his understanding of the universe beyond wormholes. An understanding that goes beyond Foster's. Selvig sees many things fast approaching and knows some of what needs to be done... but keeps getting stuck in the visions of Surtur and Ragnarok. The being that's possessing Jane might have skipped over to Darcy in the university by the time we see her meet up with Thor.
Other things Jane could know about are: Thanos, Masters of evil forming, Ultron, AIM/Hydra etc. And just how much destruction Malekith/Surtur/Kurse intend to cause with Hela overseeing it all. Aim hasn't successfully created time travel but they have a device which allows them to view the future... Jane Foster, Pym, and Selvig would repurpose this by combining it with wormhole generating technology in one of the future movies.
In the synopsis it says Thor's journey is one that leads him to reunite with Jane.
So she's there for a purpose that's tied in to the threats Thor, Asgard, and the universe are facing. Thor doesn't just decide to go visit her amidst all the chaos; and I'm doubting that Malekith or anyone goes after her, Selvig and Darcy directly. They get drawn into it... Thor meets her along the way and probably takes her/Selvig/Darcy along because they have information pertaining to one of the threats.