weaning from breast to bottle

I'll Try keep it short .. My baby is 16 weeks old tomorrow, we had a bit of a struggle with breast feeding to begin with so I would express and top up with formula. Anyways after a few weeks we were exclusively breast feeding yippee! Recently I've been expressing milk to give to her also. However I wanted to start weaning her onto formula just for one feed a day. I bought a tub of formula on Wednesday and she took it fine but then was sick EVERYWHERE in her Moses basket. So I thought I'd try again on Thursday day time and she would not take it, took a few sucks and 😖 and again yesterday and today so I guess she doesn't like the formula or the texture or the temperature but now she won't even take expressed from bottle either! Help! Does anyone have any advice on what I could do please!? I'd like for her to atleast have expressed milk!