C.S.
Hi there. Your breast milk might taste bad. Did you eat something spicy or with garlic? Are you drinking plenty of water? No sodas? Pump some of your milk and see if it is still healthy white. If this persists and baby is losing weight, get right in to the doctor and have your mil tested.
Also, look into her mouth. Does she have thrush? White stuff on her tongue and roof of her mouth? Feeding might be painful if she does and again, get to the doctor's for meds.
Your baby is telling you something, you just have to figure out what.
Try pumping out and then allowing your body to refill before next feeding and see what she does. For now, you might have to substitute with formula to keep her weight up.
Good luck. I breastfed twice and the first time it was really difficult and baby stopped wanting milk at ten months old. Broke my heart but we moved on. MY second baby never wanted to let go and I fed him for 18 months. It is a wonderful moment for you two. I hope this resolves. :)
C.