Bloodlines

[Firefoot]

Earendilyon, you say that in taking the form of an Elf, Melian's body became that of an Elf. However, her genes would still be those of a Maia. She was still Maia, just in Elvish form.

... and now he [Dior] appeared as the fairest of all the children of the world, of threefold race: of the Edain, and of the Eldar, and of the Maiar of the Blessed Realm.

Now Elros and Elrond his brother were descended from the Three Houses of the Edain, but in part also both from the Eldar and the Maiar;...

It does not include Melian as an Elf. Also, I think you might be taking it a little too literally - by saying they have Maiar blood in them probably just means that they are descended from Maiar.

Edit - cross-posting with NK. It does say she took an Elvish form:

she took upon herself the form of the Elder Children of Ilúvatar, and in that union she became bound by the chain and trammels of the flesh of Arda.