It never states she uses magic. Just that shes a healer. Potions are essentially magic let's be honest. Also the Fertility Potions & Barreness Potions were creations of the Qeteshians used/distributed by their priestesses. Most likley Edgar gets his supply from an old priestess or someone that learnt the recipe from one at least. Also why would Ziva demand to know the formula, she has read it herself that's how she cought MC in the first place. She would already know it.
Also wasent Alice's husband it was her dad that made her take the potions cos he knew he couldn't keep an eye on her 24/7.
She read the information found in Theresias diary, which only states that the formular excists, that note made us search for the recipe in the still scoldering remains of that caravan in the first place.
But it doesn't contain any details about the required ingredients and their concentration, that's all in the recipe, which is unknown to her.
We don't know where Edgar gets his Potions from exactly, but we know that Qeteshians priestess affected by the curse were widely considered witches... Zivah said so right after she turned... about how she had to move and liive in hiding because of that.
Magic is bad is the common human agenda... I don't recall hearing about a human mage before in the game.
There is a chance that humans found the formulars for the normal fertility and bareness Potions... heck even the horecock potion in one of the abondened qeteshen temples and considering it's value for different parts of society alchemists started to craft them