Yeah, she’s 7 sweeps. A troll isn’t considered an adult until likely 8 or 9 sweeps

That’s were her dreamself had been hiding the entire time, then Bec Noir killed her

We first see them with Aradia, then with Dave and Rose.

Calliope discusses them here

The self that didn’t die on the slab would die. We see this with Aradia. Aradiabot exploded when her dreamself died on the slab.

Recap 3:

“[Vriska] instructs [Tavros] to take her to her Quest Cocoon, and to kill her…”  

Quest Beds are located on the players’ planets and they need both their dreamself and original self in order to ascend

Sacrificial Slabs are located at the core of Derse and Prospit’s moons and the player only needs one of their lives left to use it

Quest Cocoon, trolls as a species didn’t have beds, they slept in Cocoons so their things were circle shaped and called Quest Cocoons until the rectangular Quest Bed

She could make anything appear and could also turn intangible 

Mental Illness™

They were killed by Jack English and Condesce while on their Sacrificial Slabs