This may sound weird, but have you tried changing the direction you're coming at her mouth from? I tried the running-nipple-up-and-down thing, and it worked a little... Until I discovered Amelia usually prefers it to slide in from the side of her mouth :-/
Everything else I wanted to say has already been said, so I'll just say this:
YOU CAN DO THIS! We all know how determined you are to do the best thing for Isla. Even when you feel like giving up, keep that in mind. We're all behind you 100%.
Sent from my iPhone so forgive the speelung misstacks
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