My son couldn't latch without the nipple shield when he was your daughter's size either. She'll get there. It's a hard road, but so rewarding. I think it's awesome that you are able to give her breastmilk this whole time mama! So many people would have given up but you are perservering!
The shooting pains in your breasts - do you think you might have thrush? If you or your daughter were on antibiotics, you're more susceptible to it. It's worth looking in her mouth and seeing if there's any white stuff in the sides of her cheek and if you think you see some, have her Dr look. If so, she needs to be treated and you need to be treated as well. I've got lots of suggestions for that, so let me know if that's it.
I'll ask in a few places and see if I can find anything about the fortifier. I'll let you know.
How is your daughter doing otherwise? How are you doing with everything else?