I learned last night that my wife has allergies.  She can't have brewers yeast or baker's yeast.   I've heard of creating a starter from just mixing and resting flour and water on the countertop for a long time.  Does this work?  Does it have the same properties as packaged yeast?

She's also, seemingly, allergic to cow's milk, but that's a whole different kettle to stir.

thanks in advance,

John