You can put it in her feed, but a 1/4 tablet B-Complex and a soft gel E are fairly small, she can swallow those no problem.
I just open the beak and pop them one at a time in the beak. Let her swallow after each one.
While vitamins are for sure not a cure all, they can sometimes offer added support to the system. Vitamin E is an antioxidant and supports neurological functions while the B vitamins help with metabolism of carbohydrates, amino acids, etc. and offers support to the legs, muscles, etc. I'd give her the vitamin support for at least 7-10 days and see if they make any difference.
The egg or tuna both contain enough selenium to help with the uptake of E and she'll enjoy a little treat. Mine love eggs, especially the cooked yolk.
Sounds like she's being spoiled. Keep us posted on how she's doing.