|There are two things ye must|
know about the wise woman
But once you try to add a second way for magic to work in the same setting you need to make them work together. For example, you need to explain why practitioners would not flock to the best one, where by "practitioners" I mean "PCs" and by "best" I mean "the one that kills monsters best".
This is pretty tricky unless you make all the changes purely cosmetic (which can be a let down for players when they realise that there is no "actual" difference) or you proceed with great care.
In AD&D, the standard system covers such a wide range of power from 1st level spells to 9th level ones that it's hard to find anywhere to fit a completely different magic system and if one did it would require a class to go with it, which also has to balance with the existing classes.
In other words: it's a total pain in the neck to have more than one magic system in AD&D and I think this is particularly the case for anything that resembles a folk-tradition with simple amulets, charms, potions, and other typical "wise woman" style magics - why would anyone bother playing such a character when they could play a normal magic user or cleric?