The chicken that is struggling in your flock is not due to size, but do to personality and differences that chickens pick on. Trying to reset the pecking order will not help. Getting a roo will not likely help.
Do you know what breed she is? You mentioned frizzled and docile.
To give this...
Are all your birds under a year old? Your Cockerels are maturing and want to be in charge of the girls. As the weather warms be on the lookout for other boys to want to fight for position. If you do not have space for roosters to runaway from each other be prepared to separate all the boys.
You may have been lucky enough to see the wiggling as the chicks got into place for hatching. At this point you wouldn't see much wiggling, but you should be watching for external pips. If you don't see them today it might just be a slight delay.
The amount of surface water required to...
I'm don't know the answer for why or what to do, but I have noticed older hens in our flock growing spurs in the past. Unfortunately after the spurs appear the birds seemed to age rapidly.
The "solid" feathers are dominant, so if one parent has regular feathers so will the chicks. They do get feathered feet and crests. I think my Silkie crosses are very pretty birds. They are hardier than the silkies. Mine are very broody, but also lay quite a bit in winter even as they age.
Although it is possible for a chick so young to have wry neck, it is not the only possibility. Not every chick hatches and unfortunately not every chick survives the stress of the first week.
Where did you get the chicks? Access the other chicks to make sure they are not declining. Make...
Occasionally we end up with a duck in one of our chicken coops. Sometimes those ducks would rather hang out with chickens than other ducks. Ducks are not susceptible to Marek's, so could work as a cross species companion. (Make sure the duck is female.)
No heat needed at that temperature. (I guess keeping birds cool is more of a concern for you).
Adding hiding places or places only the little ones fit can help.
The chicks can be very smart about how not to get pecked. I have seen my chicks push right between safe hens, but completely stay out...
The three week old chicks need heat while the older ones do not. As long as chicks can move in and out of the heat that may not matter. Some 10 week old chicks could be aggressive toward smaller birds while others of that age may not react much at all to them.
Both your setup and the...
Do not take the good egg away from the hen. Are you hoping for the hen to raise all the chicks? I know it was asked already, but the date the hen started setting and the date the incubator was started are key to what your options are.
Not everyone handles duck ratios the same.
Ducks form bonds and form territories. These bonds change throughout the mating season. Your number of drakes and hens may or it may not work fine. Adding more hens could make it better or it may not. Personally I try to keep my duck hens to drakes...