1. Allowing them to use her as a source of energy will help dispel the magic. They'll warn her that due to their inability to determine how strong the enchantment is or how much magical energy is required to dispel it, they are not able to guarantee what side effects she'll experience. If she agrees to go ahead, she may suffer some exhaustion, weakness, and vertigo. If there are additional or more severe adverse effects the group would like either for Yennefer or the others, you are welcome to propose them!

2. The god they found would be this one, though the image available in Thorne's books is an approximate sketch rather than a fully accurate illustration. He has a brief notation describing him as a comparatively newer addition to the Solvunn pantheon, and that he is connected to mirages and reflections. "New" is quite relative as many of Solvunn's old gods go back thousands of years or more.

His name is stated to be Nicodemus, Nikodaemus, or Nikodai. The mages would've attempted several pronunciations and variations before settling on Nikodaemus.

Anyone familiar with Solvunn would find his usage interesting, as Solvunn tends to favor old traditions and ancient gods. That a newer god has been invoked for a powerful enchantment indicates a deviation in their customs.