Doesn't really matter, two short people can have a tall son, two tall people can have a short son, modern biology is a statistical science, so if the author wants the mom to be tall, that doesn't have to break with any "basic biology" tenents.
APART FROM THAT, you are trying to rationalize a magical world, not trying to spill the beans or anything, but the mom is probably not who she fucking seems to be, she's a really powerful alchemist (magic user) with a big wealth of knowledge, you don't even know if she was elven nobility once upon a time, we have no idea if the protagonist is only half high elf or something, or if the mother having such a powerful connection to the "arcane" makes her more physically imposing.
TL;DR
Don't fucking apply poorly understood notions of real world science to fantasy pornography please