I have a weak chick that needed lots of TLC and her incy mate died. She was obviously lonely...lots of peeping despite food, water and warmth. I was worried that if I put her in with the rest of the hatch, she would be picked on as she is smaller and slower than they are but I gave it a try under very close supervision and she has been fine. She is clearly much happier in with her friends, is much more interested in her food and stands up ok in the line for the chick feeder. I would say that being with them has given her a greater zest for life than she had either with her one weakling friend in the incy or on her own. I have popped her out for some extra feeding....a bit of a boost with some scrambled egg and a couple of mealworms....but put her straight back in after.
If you are really concerned, you could try putting just one or two of the more robust chicks in with her....I am assuming they are from the same hatch, just healthier?