Scarlet's Master?
Also, that villian I mentioned above may want to control Tyria as well as the land he currently owns, so he may have identified the pale tree and the elder dragons as a threat so orchestrated this to eliminate them both.
Scarlet’s master? Mister E?
Omadd showed Ceara the Eternal Alchemy.
In it, Ceara saw Mordremoth and Mordremoth saw her and began speaking to her.
Ceara became Scarlet because she went mad after hearing Mordremoth.
Scarlet got out of the machine and killed Omadd on the spot.
As time went past, Scarlet got more and more voices in her head from Mordremoth and she started to research and create a plan to awaken him to get rid of the voices.
She researched dragon energy at Thaumanova, possibly blew it up to disturb the leyline it’s on but it didn’t work.
She gathered her army and placed sonar thumpers to check for a major leyline crossing and found it under Lion’s Arch.
She drilled into the leyline crossing and disturbed it so much that Mordremoth awakened.
Mordremoth is the jungle dragon and “Tyria’s new master”.
Scarlet succeeded but died doing so.
I agree with the OP i don’t think the dragon was her master. It is possible that her master did make her think it was an Elder Dragon or tried to get her to wake it up so they can destroy everything and go back to sleep soon. When that part was done her master would be able to control everything w/o the Elder Dragons getting in its way.
What if… Mordremoth IS the Eternal Alchemy!?