Sometimes some birds will need to be supplemented. If you want to try to save her, this a good place to start.
Stop garlic, garlic can be toxic to birds.
Note that her daily fluid intake needs to be no less than 23 ml per pound of bodyweight.
I understand, vets are expensive. In the house away from the others is a good place for her. It would also be best If you could keep her room warm.
If you think it might be an infection or injury that she can overcome, we can teach you how to tube feed water and food so that she does not die...
Is a vet an option?
If she has lice that sure could make matters worse, so if she has lice I recommend that treat her with permethrin dust or spray ASAP.
It does sound a lot like Marek's, but I have seen bacterial infections and coccidiosis cause paralysis. This is where a vet would be...