Breastfed baby moving to formula

HOW DO YOU DO THIS?! My daughter despised the taste and refuses it completely. I just mixed 1oz of formula with 3oz of breast milk.

She’s 5 months old, I’m back at work so I can’t be pumping/nursing like I used to. I think I I have a picky eater in my hands because she also refuses milk that has been frozen before, so I donated everything I had.... but now I don’t have enough milk for her and she refuses formula. Don’t know what to do!!!!!