Feeding help please!!!

Tomorrow will be my first day away from my 4month baby for a long period of time (6-8 hours). She’s only had breast milk. I had quite a bit of frozen milk but she absolutely refuses it if it’s been frozen before. We tried mixing it with fresh milk but she won’t take it either, so I donated all I had (almost 300oz 😭😭).

I had been working on decreasing my supply to just match what she needs daily before I realized that she wouldn’t drink the frozen stuff. Tomorrow when I’m gone, my husband is going to just give her formula. Is it ok to do that or will she refuse breast milk later? Please help!