Though talking about the lore, that had better not be regular witcher alchemy in that potion. She explicitly hasn't had the special diet, trial of grasses or the mutations so witcher potions should basically be poison she can't process at all.

Canonically she's witcher trained but not subjected to any of the mutations, but she's also of the Elder Blood and a Source. So compared to a traditional witcher you'd expect her to be slower and weaker (because she lacks the mutations) but have greater access to magic (because she's a Source). You'd also expect her to use most witcher tools and gadgets, but not potions (because they should just be poison to her, not having the altered gut of a witcher).

Don't know anything about the Witcher, but assuming that it is as you said, than that's a good thing.