A couple of thoughts.... When she's fussing, is it because she has trapped air and is uncomfortable? I would take her off the breast and burp her, let her settle a bit and then put her back on the same side. I would also do breast compressions after your flow has slowed a bit to keep her interested in feeding (ie. she may be fussing because the flow is too slow for her liking). If you put her on the other side, will she latch and feed? Lastly, how long has she been feeding like this! There is a 4 mo gs that can be quite brutal so if this is a recent thing, it might just be the gs and she should settle down in a few days.