Think really the main themes of first edition Kaeris was Accelerant, Resource Management, Immolate and the trigger Turn It Up. These were unique to her and it would be nice if those at the least stayed into the new rules.
With the new 3 actions per master and way soulstones now work, mind, there is a chance Turn It Up could become a bit overwhelming - that's a lot of burning tokens flying around and a ton of shots in one activation. Flamewall would likely be present on an upgrade, same as the way Sonnia gets the spell.
As for Avatar, I'm doubting following the fluff in book 3 that Kaeris is all that safe for anyone to be near in a combat situation. She doesn't seem to plan ahead what she's going to next. It'll certainly be fire oriented, but whether the flame element of the avatar would have a controlled form like a Phoenix may well be doubtful, I'd like to see such a model though.