I'm sorry that she's not doing very well.
Heat can be hard on them, so I'd watch to make sure she's getting plenty to drink and has shade.
The balance issues may be with her all her life it seems. You can always start her back on the vitamins for a while and see if they help.
I agree, she...
Hard to know, but I do agree, there's something a little off about her in the photos. Perhaps genetics, something developmental. I don't think it's anything that you can corrected. Giving support through vitamin therapy and seeing that she's eating/drinking well, etc. may be the best you can do.
I'm glad to hear Einio is doing a little better and getting stronger.
When you get a chance, take some current photos of her and how she stands - you mention her hocks (joints?) are close together, is she like knock kneed? Perhaps she has a developmental or bone deformity but hard to know if...
I wouldn't worry too much about the comb. Unless you bought them from a breeder that adheres to the SOP, then likely you're going to have some variation in the comb.
I've had SLW (hatchery) that had the divot of dent and with a spike, so I'd just chalk it up to having a mixture within the breed.
LOL She KNEW you were up to something😂
The extra B vitamins won't hurt the others at all, it may be good for them.
When I give a tablet or partial tablet to a bird, I just take them aside, pull down on the wattles or lower beak, open the beak slightly and shove the tablet or pill inside...