Devil's Advocate here:
In her defense, Igarashi was pretty much acting like a small kid asking for attention, but with the great difference being that he's a very large man now, not to mention that Chiyo was busy preparing the food and holding a knife, which in japanese culture is considered as dangerous and ought to remain undisturbed lest you want an accident, hence why she was being so curt (well, more than usual).
Besides, you need to remember that she won't change her personality and become tamed overnight or, for that matter in this story's time, after just a couple months: this has been her personality for years and it's gonna take some time for her to be more affectionate and less, well, bitchy. You will have an easier time reading this manga by simply treating their relationship as a "golden retriever" dog dating a "norweigan forest" cat (or any other kind of coy cat).
Also, about the Ookuma issue, what is she exactly supposed to tell them? "By the way, once in the past I knew that guy and was very friendly with him but then some rumors started going on and he snubbed me due to that and we never talked again". They weren't dating nor anything of the sort, at most they were a "koibito miman" (and that would be pushing it) but that's it, she would end up causing needless drama in a society that instills you to never cause problem for people or in public and potentially ruin Igarashi's friendship with his coworker, not to mention also breaking one of her best friend's heart; that girl is pretty much screwed an can only hope that after some years pass she won't have to meet him again like she did up until Igarashi came into her life.