Much smaller than the rest

Hi! I feel like this is a sort of question that is asked a lot. But one of our four checks is much smaller than the other. She's a brown leghorn and is much smaller than the white leghorn and the other two which are an Americana and a barred rock. She does not seem to socialize very much but she will run under the other chicks wings at times. But if she is not doing that she just stands in a corner. She definitely does not eat like the others and seems to just pick out a morsel every once in a while. My question is should I give her time alone in a Nother during the day? Or should I just keep her in there to socialize with her sisters? They are will all be four weeks in two days and we have had them for about 10 days. Thanks for reading