Whenever I see respiratory infection I think of secondary infection caused by something else like cocci or worms. Seeing as your chick is on the ground, I would take it inside and treat it for both cocci and worms and see how it reacts.
I did have one chick last year that was doing something similar to yours that I finally gave up on. Brad Legg told me to cull it, I couldn't do that and I couldn't keep making it a pin cushion with all the injections either, I had given it multiple round of every med I could think of. I finally gave it to @thndrdancr for homeopathic treatment. I believe the last time she mentioned its condition that she said it may be a birth defect which is what Brad had suggested as well.
I have a video of it, but I am not savvy enough to post it.
Most likely respiratory. I do have an adult purple black shoulder silver pied that breathes like this. Painful to watch but she breeds and thrives. I always wonder how she sleeps?
I have had them have it be respiratory disease or even gapeworm. At least gapeworm is easily treatable.
Have you checked inside her mouth? I think canker/thrush presents itself that way as well. Also called trichinamniasis.
The little one kskingbee gave to me is thriving and seems happy, but she is actually missing or is not formed correctly in the tongue/glottis area, so it is a birth defect. poor dear probably kept wondering why you kept dosing her with nasty stuff.
prob. gape or a type of capillaria worms, you can try levasole or ivermectin.
the link below says fenbendzole for the gapes, I find the product prohibit ( levasole active ingredient ) works nice and quick .
Because it 's a respiratory disease for sure ... even if it is a secondary disease. If I do not treat the respiratory disease ....my bird will die , worm problem is not so fuliginous !