Your "Stress Aid" link does go to drugs.com Canada - I see it should be labeled for poultry, turkey, cattle, swine, etc. It does contain B2 (Riboflavin), but it is a Vitamin/Electrolyte product that should not be used for a long period of time. Personally, I would not use it for more than 2-3 days a week. (for a sick bird)
https://www.drugs.com/vet/stress-aid-can.html
If you wish - post a photo of the exact product you have - both front and back.
Human B-Complex, can also be used - do you have a local pharmacy that carries vitamins?
Being in Canada, sometimes it's harder for us in the US to make specific recommendations on products available to you. It may be better to show us photos of products that you have found and are considering.
I'm sorry that your pullet is having trouble walking. Posting the video when you can, may be helpful.
Tell us about what you feed including treats.
Sometimes it's very hard to know if a chicken has disease unless you lose them and have some testing performed.
Look forward to more information and photos/video.