I am SO sorry to hear this setback. I know exactly how frustrating it is. I almost lost my supply completely at 10 days, because after I got her back on the breast at 5 days, she was sucking ineffectively. Between 5 and 10 days, she lost 10 oz
and I had almost no milk left. That's when I started pumping too. She also started refusing the breast then, getting mad and beating my breast when I offered it. I guess she got so frustrated at being hungry. 
I got my supply back by using a hospital grade pump and pumping often, and taking fenugreek and blessed thistle, 4 tabs 3 times a day, plus domperidone, 10mg 4 times a day. I highly recommend the herbs! It was crazy hard work and I felt like such a failure, but it DID work. One thing they recommended (which didn't work for me, but may for you) was to supplement at the breast with the tube. Since my baby girl was refusing to even consider latching, I couldn't, but yours is still using the nipple shield so it may work for you. That way you would still be feeding her at the breast, and I know how much that helps psychologically at this point. Even if you used bottles for the bulk of the milk, you could do this sometimes, to remind her where the milk comes from.
I know how time consuming it is to both pump and nurse/finger feed. At the worst point, I was doing one or the other for 21 hours a day, and got 3 hours sleep in 20 minute spurts between each round. Bottles really helped both of us to get some much needed sleep, and helped my LO gain some weight. It felt like the end of our nursing relationship to accept using them. But they are just another tool, and if they help her to get bigger and stronger, in time, she can get back to nursing. My DD was exclusively bottle fed from 10 days to 3.5 weeks, which works out to about 2 weeks, and she did latch after that. And in the meantime, remember that she is still being nourished by your body. And THAT is only because you are SUCH a dedicated mother who is willing to work this hard to give her that.
Its SO hard now that it barely feels possible. I know. But when you look back on it later, you will realize how short a time it really was, and how much it was worth all the work. You CAN get past this hurdle!
If you need to talk or vent or whatever, I am available.
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