I dont know if it would help, but I was having a similar problem that was starting to lead to breast refusal because of fast flow (but this was at about a week old)

Have you tried a nipple shield? It may be a PITA, but it may control the flow just enough for her to learn to cope and when she's bigger she can just wean off them?

My DD did that (my boob was also abit big for her, so it was for both issues combined really) and she's now feeding really well - even without the shield now!

HTH Hun, I know how frustrating it is when bubbas can't cope with the flow