Could Kana really tell Shinichi's Migi apart from the other Parasytes, or was she just delusional?
TL;DR: It is possible, though the manga is never conclusive about that.

@senshin I think Migi is able to tell one parasite from another, at least that is the case for a certain parasite. The proof is given on Page 194 in Volume 9 of the manga:


   


So if Kana can reach the level of Migi in detecting and differentiating the signals emitted by the parasites, then she would probably be able to tell Shinichi and Migi from the other parasites. Kana demonstrated her potential with her incredible sensing ability on Page 75 in Volume 5 of the manga:


   


And on Pages 115 and 120 in Volume 5 of the manga, we saw that her powers have evolved.


   


Then there is her dream, in which Shinichi is clearly distinguishable from the other parasites. Conclusion: it does seem promising that Kana might eventually be able to tell Shinichi and Migi from the other parasites had she not rushed to her death at the hands of a parasite when her powers were still immature.