She's a calm but sassy... toad! (A toad humanoid, they are an actual species of Argonian) . She is a very ancient creature that exists in every dimension of the world. She spoke with the player yesterday, she talks to the play in the present and she knows what she's going to talk to the player about tomorrow. She has a deep and wise voice, but dont forget that she is a toad.
We imagine she'd have some sort of croakyness to her voice, like a toad. Therefore perhaps some vocal fry in the voice. A reference could be Ornifex: https://www.youtube.com/watch?v=-BqapSWDH-M&t=37s -- where the actress is adding bird influences, we'd like it replaced with toad influences. But -- just as in that reference -- note that the voice includes non-vocal fry parts -- therefore, avoid overdoing vocal fry.
Accent - American or British