I don't know for sure if this could help or if the angles of your chickie's beak would allow it, but you may want to try physical therapy and taping the beak in place at night. I've gotten significant improvement for my little girl doing this. If you are able to gently move her beak into the correct position or very close to correct, then I think it's possible you could achieve some improvement.
My chick is 7 1/2 weeks old. She hatched with crossbeak and parrot beak (short lower beak), and with rapid change and growth, she was quickly unable to forage and was well on her way to having serious difficulties eating her feed, but she can now forage again and is doing very well!
I'm still working through this all and am not positive that it will be a cure of any kind. My hope is that once she stops growing, the corrections I make now during growth will maintain and be permanent, but I don't know if that will happen. Hopefully at the least, it will be a simpler form of maintenance...
I felt I needed to share what experience I have so far in hopes of helping your chickie, if possible. I think you may have a very good chance of quickly improving your chickie's quality of life!
Unfortunately, I don't have any good photos before taping... I wasn't expecting such quick results. Here she is on September 28th, the day after I started taping. Her beak had slipped back all the way to where it was before taping the night before.
View attachment 4238664
View attachment 4238665
Two days later on September 30th, her beak is already maintaining improvements...
View attachment 4238666
View attachment 4238667
View attachment 4238668
October 6th, she's foraging again! It made my heart so happy to see her joyfully grasping grass...
View attachment 4238669
October 9th...
View attachment 4238670
View attachment 4238671
View attachment 4238672
I first tried physical therapy alone, but even with multiple times a day, it wasn't enough to keep the changes in check and then I found this post:
https://www.backyardchickens.com/th...r-flock-today.1371402/page-1284#post-27058382 where
@ChicksnMore used tape to correct a crossbeak successfully. I didn't realize at first that it was a crossbeak caused by an injury (rather than a birth defect like mine has), but I had nothing to lose, so I tried it.
After the first night I taped, her beak was very close to correct the next morning, but within an hour it was back to where it was before taping... the next day it was good for a little over an hour... and each day it continued to stay in place longer until it was maintaining all day in a correct or near correct position.
She came down with coccidiosis (she's since recovered) and I stopped the taping for a few days to avoid any added stress with the extra handling. It was also becoming hard to keep the tape in place with the short beak, so as a result of those two things she had regressed a bit, but I'm working on managing/correcting the parrot beak as well and will put together a more detailed thread on her journey once I have more to show.
Here's our routine...
Every evening after she's gotten a good fill of feed and is ready to roost, I do physical therapy for 15 minutes. I wrap her in a towel to hold her still and keep her comfy and gently but firmly push the lower beak a little past the correct position and hold it for as long as she'll let me, usually only a couple of minutes (or a few seconds!) at the most... or I will just repeatedly push and release in a gentle fluid motion. At first it feels a bit stiff, but quickly loosens up and the movement becomes soft and easy. She often snoozes while I do this.
Then I tape the beak closed with the lower beak as correctly aligned as possible using a thin strip of kinesiology tape. I avoid covering her nares (nostrils) and tape tight enough that the beak can't open or come loose. There's a little fussing during taping most nights, but she quickly relaxes and there's no fighting. Then I pop her onto a roost in a dark box with her siblings for the night. Right now she's getting 12 hours in the tape. I often check her just to make sure the tape hasn't slipped before I go to bed.
Here's what the taping looks like...
View attachment 4238673
View attachment 4238674
In addition, to the physical therapy and taping, I do trim her beak as needed. I just trim any overgrowth that becomes too long and hinders proper closure of her beak, using the "quick" as my guide and keeping it a short length beyond it, to avoid bleeding. I like using an electric manicure tool because it's small and lightweight.
https://www.amazon.com/Alety-Electric-Portable-Professional-Manicure/dp/B0C2V6SMFY
Here is a link to the tape I use:
https://www.amazon.com/OK-TAPE-Kinesiology-Therapeutic-2in×16-4ft/dp/B0BJ248CVZ
I hope this helps!