if you wana continue feeding her formula i suggest you change to other brand as my gal have this problen too when i stop bf her n give her formula she also pass out alot if the brand is not suitable for her till we change to s26 then it stop ..you can actally request sample from different brand of milk powder online to try before purchasing it .
in another way for your breast milk try eat more milk booster food like oats , salmon , cod fish , cheese cake and many others and power pump every 2 hrs it will help and boost your milk fast