You need to change to a Avian Qualified Vet or better a Certified Avian Vet!!! Your current Vet is likely a General Vet, does care and wants to help, but likely does not have the training needed to provide in depth care of a Parrot, especially a larger Parrot like a MAC.
Your MAC should have had a Full Spectrum Blood Screen based on the Medication selected (see near end of Post).
Sorry, but this could /will be seen as hard hearted. But, you have a sick MAC and knowledge of what your Vet's background is, tests in fact taken /provided, findings as part of each visit, and lastly providing it with clarity is important for you to know and have!
The Parrot Forum is a gathering of Parrot owners with a wide across-section experiences, which allows individuals and the group as a whole to provide support and guidance regarding the care and ownership of a wide cross-section of Parrots. Members are not trained Vets nor Vet Specialists.
1: Any visit to a Vet (Generalist to Specialist), one should always be provided with a document that defines the visit and after visit care. This document is commonly a single page for a normal yearly visit. A sick Parrot visit is commonly multiple pages.
2: Never leave without receiving specific instructions and hands-on training on providing medication when determined as part of the visit.
3: With a sick Parrot visit, a follow-up visit is scheduled and a clear description of what requires a quick return.
4: Any medication provided should come with a verbal and written reason what the medication is, why it is being provided and specific side-effects to watch for. In all cases, whatever medication is provided, all of that medication must be used completely, even if the Parrot does improve.
The Sad Truth, and this is with near all of us, is that we are not able to clearly hear and remember what the Vet has stated verbally and that is why it is so important to receive a Visit Document, which covers the Visit and what was found.
In all cases, always Web Search whatever medication is prescribed, so that you have a clearer idea of what the medication will provide.
Sadly, my recommendation is that you need to return to a Vet with Avian Training with your MAC 'ASAP' for an additional Visit. This should include both of you and your MAC. Please be honest with your Vet that the emotions of seeing your baby being sick is clouding your mind and you will need information written down!
I have been dealing with Very Sick Amazons for over 45 years and with all the knowledge over all the years, I to this day, can draw a blank when things are really bad. So, I always get a written document! No shame, its just being honest about ourselves and what is needed to assure the good care of our Parrots.
My readings of your Thread and Posts show that your current Vet is stepping told a specific direction that implies that your MAC has an infection of the Airway and/or Lung (air sacks). Infections of this Nature are not to be taken lightly! Yes, this could be used as a general, but more commonly for airway and air sacks.
At this next visit:
a. Have your Vet show you how to properly handle and hold your MAC. It is not uncommon for it to take two Humans to hold and provide any oral medication and/or support feeding!
b. If not completed as part of an earlier one of this series of visits, requested a full blood spectrum test.
c. Get a written document
d. Set-up a return visit
Buy a Gram Scale with stand for your MAC. Take weight readings each morning after her first moment and before she eats. Write it down with day, time and weight.