It was entirely possible, easy, in fact, for Eldrian to obtain approval for Diane to teleport over. Vivian might struggle, but she was on friendly terms with Pelaros and Myropsis. If she asked for their aid, it was entirely possible for things to be arranged. Which meant they could even waive the initial 100 gold cost.
Vivian had also earned quite a bit of earnings. Her aura, whatever it may be, was incredibly effective at killing the undead and cleansing areas with miasma. She would even be able to pay the advanced cost and all—should it be required.
Since Vivian had asked Eldrian for a match, and brought him out here, far away from civilization, it didn't take a genius to know her motive.
She wanted to test herself.
