Welcome to the fun zone, trying to do any such idea is very hard. Best I could suggest is making the ears extra pointy and a bit long, and also giving leaf clothing or some such. The best way to convey it honestly might be to do the inverse, weakening some of the succubus aspects. Maybe make the tail shorter and the horns relatively small, or do something like only having the tail.
Maybe have the succubus parts appear like twigs or something spiritual or something, being influenced by the elf blood. Though at least elves have an identifier, dwarves don’t even get that. Yeah sure, male dwarves have impossibly huge beards and unusually short statures for men, but female dwarves? It’s just a short girl.