This happened to us. When they are alone, they seem to crow as if to say "is anybody else out there?!". We got a batch of 6 chicks and introduced them a little bit at a time starting at 5 weeks. She stopped crowing and was so happy to have company...she wasn't agressive but she did show her status as #1 chicken. Unfortunately for us, that batch turned out to be all boys. Once we rehomed them, she started to crow again. The second time around, we got what ended up to be pullets. We introduced them much sooner since our hen was so lonely. I just felt so sorry for her!!
I would definitely wait to make sure your new chickens are healthy. Introduce them gradually...watch and make sure there are no major scuffles. There will be some pecking, but it likely won't be anything major. She was there first, so she will establish her order as being on top. The newbies will be afraid and will bow down to her. She will probably stop crowing. Mine did...and we haven't heard a crow out of her since. The group is getting along great and she is happy to not be alone any more!!
Good luck!
