I agree with Clockwork. I guess I don't get the Sonnia burning vs. non-burning argument.
Yes she doesn't have the synergy of some other condition masters, but the burning tokens help.
I usually bring Witchling Stalkers and a Handler because they are excellent models for the price and just so happen to help Sonnia with burning, not because they burn. I have summoned stalkers and it is nice when it happens, but I don't plan on that as a necessity.
So I suggest you not making a "burning list", but don't shy away from some models that would be in that list if you don't make a "burning list".
Also, Sonnia brings many more options than Perdita.