Neocate for 6.5 month old ( Fortifying BM)

Y’all this mama needs help. So we are seeing a GI specialist and she gave us neocate for me to fortify my breastmilk (there isn’t enough fat in my milk) bc my LO is not growing at a good rate and is falling off her growth chart (now 13.8 lbs). No matter what I do, she does not want to drink it. I’m trying my best. I do plan on reaching out to her doctor soon to inform them that this isn’t working because I know if she doesn’t gain, they will need an explanation.

How can I “fatten” her up. I really feel like a failure because of this😭