Oh this is cool.

So a god dies and creates a whole ecosystem.

Yep! There was already some life when she arrived, but her lifeblood & direction guided it as she slowly (on her timescale) died. This process probably took (hundreds of?) thousands of years, tbh. I haven't settled that 100% but it would make sense that the timescale of a deity would be very different from other life.

this is so cool owo

With water being a good conductor of magic is there a like, anemia equivalent in the world where folks' genetics determine how well their blood can intake magic?

-Signed, an anemic motherfucker

Hmm there are probably people that are worse at conducting magic- but what that amounts to is someone who is magically-speaking "dun". They're incapable of absorbing / holding ambient magic (mana) for direction with spellwork.
They could still be an accomplished runesmith, magitech, alchemist, etc. But direct manipulation of magic would be outside their reach.

Humanoids in particular don't need or benefit from magic (its usually dangerous in large concentrations, akin to radiation), so unlike anemia you wouldn't suffer from not having it or being insensitive to it. You'd probably do better in a lot of dangerous professions, tbh.