Really good advice above. Using a supply line (lactaid/SNS) is a really great idea. This would really help with the nipple confusion, but stop the feeling you were making her go hungry.

It's so hard because it's such a slipperly slope. If you think of it that every bit of formula she drinks is a signal your body is not getting to make more milk, so that vicious cycle of low supply starts. Plus every bottle feed she has adds to nipple confusion and her learning bottles are easy so more likely to start refusing the breast.
Supply line feeding would cut both those problems right down, she would stimulate your supply the whole time she was drinking formula, because she could get it while sucking at the nipple still, thus increasing your supply each time, and (hopefully!) lessening the amount of formula day by day.

I'd definitely look at getting onto motilium too. As well as resting heaps, drinking well, get someone to bake you up lactation cookies and eat loads, eat up on porridge and nuts and look into fennugreek and other supplements that help supply.

I wouldn't ever express for 120min either. Won't do as much for your supply as shorter, but more frequent expressing would, and sooo tiring for poor you. Don't be too disheartened by the amount either, it's not neccessarily a reflection of what she gets.

Also - get skin to skin with your bubba! As often as you can. This is great for your supply and getting past any frustration and nipple confusion etc.

All the best!